Patent Publication Number: US-8972315-B2

Title: Apparatus and methods for activity-based plasticity in a spiking neuron network

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-owned U.S. patent application Ser. No. 13/152,119, entitled “SENSORY INPUT PROCESSING APPARATUS AND METHODS”, filed on Jun. 2, 2011, co-owned and co-pending U.S. patent application Ser. No. 13/465,924, entitled “SPIKING NEURAL NETWORK FEEDBACK APPARATUS AND METHODS”, filed May 7, 2012, co-owned and co-pending U.S. patent application Ser. No. 13/465,903 entitled “SENSORY INPUT PROCESSING APPARATUS IN A SPIKING NEURAL NETWORK”, filed May 7, 2012, a co-owned U.S. patent application Ser. No. 13/465,918, entitled “SPIKING NEURAL NETWORK OBJECT RECOGNITION APPARATUS AND METHODS”, filed May 7, 2012, a co-owned U.S. patent application Ser. No. 13/488,106, entitled “SPIKING NEURON NETWORK APPARATUS AND METHODS”, filed Jun. 4, 2012, a co-owned U.S. patent application Ser. No. 13/488,114, entitled “SPIKING NEURON NETWORK APPARATUS AND METHODS”, filed Jun. 4, 2012, a co-owned U.S. patent application Ser. No. 13/541,531, entitled “CONDITIONAL PLASTICITY SPIKING NEURON NETWORK APPARATUS AND METHODS”, filed Jul. 3, 2012, co-owned U.S. patent application Ser. No. 13/660,923, entitled “ADAPTIVE PLASTICITY APPARATUS AND METHODS FOR SPIKING NEURON NETWORK”, filed herewith on Oct. 25, 2012, co-owned U.S. patent application Ser. No. 13/660,945, entitled “MODULATED PLASTICITY APPARATUS AND METHODS FOR SPIKING NEURON NETWORK”, filed herewith on Oct. 25, 2012, and co-owned U.S. patent application Ser. No. 13/660,982, entitled “SPIKING NEURON SENSORY PROCESSING APPARATUS AND METHODS FOR SALIENCY DETECTION”, filed herewith on Oct. 25, 2012, each of the foregoing incorporated herein by reference in its entirety. 
     COPYRIGHT 
     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present innovation relates generally to computer vision and machine learning using artificial neural networks, and more particularly in one exemplary aspect to computer apparatus and methods for processing of sensory data using pulse-code neural networks. 
     2. Description of Related Art 
     Artificial spiking neural networks are frequently used to gain an understanding of biological neural networks, and for solving artificial intelligence problems. These networks typically employ a pulse-coded mechanism, which encodes information using timing of the pulses. Such pulses (also referred to as “spikes” or ‘impulses’) are short-lasting (typically on the order of 1-2 ms) discrete temporal events. Several exemplary embodiments of such encoding are described in commonly owned and co-pending U.S. patent application Ser. No. 13/152,084 entitled APPARATUS AND METHODS FOR PULSE-CODE INVARIANT OBJECT RECOGNITION”, filed Jun. 2, 2011, and U.S. patent application Ser. No. 13/152,119, Jun. 2, 2011, entitled “SENSORY INPUT PROCESSING APPARATUS AND METHODS”, each incorporated herein by reference in its entirety. 
     Typically, artificial spiking neural networks, such as the network described in owned U.S. patent application Ser. No. 13/541,531, entitled “CONDITIONAL PLASTICITY SPIKING NEURON NETWORK APPARATUS AND METHODS” and incorporated herein by reference in its entirety, may comprise a plurality of units (or nodes), which correspond to neurons in a biological neural network. Any given unit may be connected to many other units via connections, also referred to as communications channels, and/or synaptic connections. The units providing inputs to any given unit are commonly referred to as the pre-synaptic units, while the unit receiving the inputs is referred to as the post-synaptic unit. 
     Each of the unit-to-unit connections may be assigned, inter alia, a connection efficacy, which in general may refer to a magnitude and/or probability of input spike influence on unit output response (i.e., output spike generation/firing). The efficacy may comprise, for example a parameter—synaptic weight—by which one or more state variables of post-synaptic unit are changed. During operation of a pulse-code network, synaptic weights may be dynamically adjusted using what is referred to as the spike-timing dependent plasticity (STDP) in order to implement, among other things, network learning. In some implementations, larger weights may be associated with a greater effect a synapse has on the activity of the post-synaptic neuron. 
     In some prior art visual processing implementations, such as illustrated in  FIG. 1 , a spiking neuron network in may comprise one or more identical neurons. During operation, the neurons of the network may evolve based on the neuron adaptation process and the input, illustrated by the frame  102  in  FIG. 1 . The input may comprise one or more objects and/or features  104 ,  106 . Some of the features may be less frequently present in the input (e.g., the horizontal feature  104  in  FIG. 1A ) compared to other features (e.g., such as vertical features  106  in  FIG. 1 ). In some applications it may be of benefit to quickly identify salient (e.g., less frequent) features in order to, for example, instruct a saccading module of a visual processing system to transition (saccade) to the salient feature. Such salient feature selection may also be referred to as formation of a “pop-out”. 
     As a result of network operation, the neuron population of the network may evolve to comprise two (or more) different types of neurons, as depicted by squares  116  and circles  114  in  FIG. 1 . The neurons of different types may be randomly distributed and randomly connected via connections  118 , as illustrated by the network snapshots shown in the panels  110 ,  140  in  FIG. 1 . The neurons  104 ,  106  of the network may evolve to form receptive fields, e.g., depicted by broken line rectangles in  FIG. 1 . As the vertical features are more frequent in the input  102 , more of the receptive fields may select a vertical feature, as shown by the receptive field map  120  in  FIG. 1 . In some realizations, the receptive fields may fail to form, and/or may select the wrong objects (e.g., the background shown in the panel  150 ). The receptive field map  150  of  FIG. 1  does not contain a pop-out. 
     Some existing approaches utilize re-wiring of the network during operation in order to, for example, identify salient features (cause pop-outs). However, such processes may be computationally intensive, as the network composition may change rapidly based on the input. Accordingly, manual identification rewiring of a network comprising many neurons of different types that is capable of real time visual processing may require computational power that exceeds the capability of video processing devices, particularly portable devices. 
     Consequently, there is a need for an improved plasticity mechanism to adaptively affect network connectivity in order to realize a spiking neuron network capable of reliably identifying salient features within a wide variety of inputs. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure satisfies the foregoing needs by providing, inter alia, apparatus and methods for implementing adaptive plasticity in spiking neuron networks that may be dynamically adjusted in accordance with the connection activity thereby enhancing performance of a neural network. 
     In one aspect of the innovation, a signal processing apparatus comprising a storage medium is disclosed. In one embodiment, the storage medium includes a plurality of executable instructions configured to, when executed, determine plasticity rule in a spiking neuron network by at least: determination of an intra-similarity measure between outputs of neurons of first portion of the network; determination of an inter-similarity measure between outputs of neurons of the first portion and neurons of second portion of the network; configuration of the plasticity rule based on a combination of the intra-similarity and inter-similarity measure; and adjustment of an efficacy of one or more inhibitory connections between neurons of the network in accordance with the plasticity rule. 
     In another aspect, a method of updating efficacy of computerized interface for a spiking neuron. In one embodiment, the method includes, for an input stimulus representative of a first feature and a second feature: potentiating the interface in accordance with a plasticity rule when the interface is configured to provide an inhibitory indication from a neuron of a first type to a neuron of a second type within a network; and depressing the interface in accordance with the plasticity rule when the interface is configured to provide an inhibitory indication from one neuron of the first type to another neuron of the first type within the network. 
     In one variant, the rule is based on a combination of an intra-similarity measure and inter-similarity measure, the intra-similarity measure being based on a similarity measure between responses of neurons of a first portion of the network, and the inter-similarity measure being based on a similarity measure between responses of neurons of the first portion and responses of neurons of a second portion; neurons of the first portion are configured to respond to the first feature; neurons of the second portion are configured to respond to the second feature; the one or more inhibitory connections comprise first group of inhibitory connections disposed in-between neurons of the first portion, individual ones of the first group of inhibitory connections configured to provide an inhibitory indication to one neuron of the first group based on a response of another neuron of the first group to the first feature; and the plasticity rule is configured to increase efficacy of individual ones of the first group of inhibitory connections. 
     In another aspect, a computerized visual input processing system is disclosed. In one embodiment, the system includes: a sensing array configured to acquire a plurality of frames of a visual input representative of first and second features; and a spiking neuron network. In one variant, the network includes: a plurality of neurons configured to generate one or more responses based on individual ones of the plurality of frames; and a plurality of connections configured to provide inhibitory signals to individual ones of the plurality of neurons based on the one or more responses. 
     In another variant, individual ones of the plurality of neurons are configured to be operable in accordance with a response process capable of causing: a first portion of the plurality of neurons to generate at least a portion of the one or more responses based on the representation of the first feature; and a second portion of the plurality of neurons to generate at least another portion of the one or more responses based on the representation of the second feature; and individual ones of the plurality of connections are configured in accordance with a plasticity rule based on a combination of an intra-similarity measure and inter-similarity measure, the intra-similarity measure being based on at least responses of neurons of the first portion of the network, and the inter-similarity measure being based on at least responses of neurons of the first portion and responses of neurons of the second portion. 
     In another embodiment, the system includes a sensing array configured to acquire a plurality of frames of a visual input representative of a plurality of features; and a spiking neuron network comprising: a plurality of neurons configured to generate one or more responses based on individual ones of the plurality of frames; a plurality of inhibitory connections configured to provide inhibitory signals to individual ones of the plurality of neurons based on the one or more responses; and adaptive plasticity logic configured to aid selectivity during network operation such that an efficacy of individual ones of the plurality of inhibitory connections between neurons responding to similar ones of the features is increased, while an efficacy of individual ones of the plurality of inhibitory connections between neurons responding to different ones of the is reduced. 
     Further features of the present disclosure, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram depicting feature identification by an artificial spiking neural network according to the prior art. 
         FIG. 2  is a block diagram depicting image processing apparatus comprising activity based salience map generation, in accordance with one or more implementations of the present disclosure. 
         FIG. 3  is a graphical illustration of exemplary salient feature types useful with the image processing apparatus of  FIG. 2  according to one or more implementations. 
         FIG. 4A  is a block diagram depicting an artificial spiking neuron network according to one or more implementations. 
         FIG. 4B  is a block diagram depicting encoder unit specificity attainment and plasticity development during training, according to one or more implementations. 
         FIG. 5  is a plot presenting simulations data illustrating activity based plasticity for use for example in the processing apparatus of  FIG. 2 , in accordance with one or more implementations. 
         FIG. 6A  is a block diagram depicting salient feature detection by an artificial spiking neuron network comprising neurons configured to respond to different features, according to one or more implementations. 
         FIG. 6B  is a plot depicting a saliency map obtained using adaptive plasticity methodology of the disclosure, according to one or more implementations. 
         FIG. 7  is a logical flow diagram illustrating a method of determining an adaptive plasticity mechanism, in accordance with one implementation. 
         FIG. 8  is a logical flow diagram illustrating a method of determining adaptive plasticity for a spiking neuron comprising multiple input connections, in accordance with one implementation. 
         FIG. 9  is a logical flow diagram illustrating a method of connection plasticity update based on the adaptive STDP rule, in accordance with one implementation. 
         FIG. 10  is a block diagram illustrating a sensory processing apparatus comprising an adaptive plasticity mechanism in accordance with one implementation. 
         FIG. 11A  is a block diagram illustrating a computerized system useful for, inter alia, providing an adaptive plasticity mechanism in a spiking network, in accordance with one implementation. 
         FIG. 11B  is a block diagram illustrating a neuromorphic computerized system useful with, inter alia, adaptive plasticity mechanism in a spiking network, in accordance with one implementation. 
         FIG. 11C  is a block diagram illustrating a hierarchical neuromorphic computerized system architecture useful with, inter alia, adaptive plasticity mechanism in a spiking network, in accordance with one implementation. 
         FIG. 11D  is a block diagram illustrating a cell-type neuromorphic computerized system architecture useful with, inter alia, adaptive plasticity mechanism in a spiking network, in accordance with one implementation. 
         FIG. 12  is a graphical illustration depicting histogram determination based on post-synaptic and pre-synaptic activity of a unit of the spiking network of  FIG. 4B , according to one implementation. 
     
    
    
     All Figures disclosed herein are © Copyright 2012 Brain Corporation. All rights reserved. 
     DETAILED DESCRIPTION 
     Implementations of the present technology will now be described in detail with reference to the drawings, which are provided as illustrative examples so as to enable those skilled in the art to practice the technology. Notably, the figures and examples below are not meant to limit the scope of the present disclosure to a single implementation, but other implementations and implementations are possible by way of interchange of or combination with some or all of the described or illustrated elements. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to same or like parts. 
     Where certain elements can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the various features of the present disclosure will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the disclosure. 
     In the present specification, an implementation showing a singular component should not be considered limiting; rather, the disclosure is intended to encompass other implementations including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. 
     Further, the present disclosure encompasses present and future known equivalents to the components referred to herein by way of illustration. 
     As used herein, the term “bus” is meant generally to denote all types of interconnection or communication architecture that is used to access the synaptic and neuron memory. The “bus” may be optical, wireless, infrared, and/or another type of communication medium. The exact topology of the bus could be for example standard “bus”, hierarchical bus, network-on-chip, address-event-representation (AER) connection, and/or other type of communication topology used for accessing, e.g., different memories in pulse-based system. 
     As used herein, the terms “computer”, “computing device”, and “computerized device” may include one or more of personal computers (PCs) and/or minicomputers (e.g., desktop, laptop, and/or other PCs), mainframe computers, workstations, servers, personal digital assistants (PDAs), handheld computers, embedded computers, programmable logic devices, personal communicators, tablet computers, portable navigation aids, J2ME equipped devices, cellular telephones, smart phones, personal integrated communication and/or entertainment devices, and/or any other device capable of executing a set of instructions and processing an incoming data signal. 
     As used herein, the term “computer program” or “software” may include any sequence of human and/or machine cognizable steps which perform a function. Such program may be rendered in a programming language and/or environment including one or more of C/C++, C#, Fortran, COBOL, MATLAB™, PASCAL, Python, assembly language, markup languages (e.g., HTML, SGML, XML, VoXML), object-oriented environments (e.g., Common Object Request Broker Architecture (CORBA)), Java™ (e.g., J2ME, Java Beans), Binary Runtime Environment (e.g., BREW), and/or other programming languages and/or environments. 
     As used herein, the terms “connection”, “link”, “transmission channel”, “delay line”, “wireless” may include a causal link between any two or more entities (whether physical or logical/virtual), which may enable information exchange between the entities. 
     As used herein, the term “memory” may include an integrated circuit and/or other storage device adapted for storing digital data. By way of non-limiting example, memory may include one or more of ROM, PROM, EEPROM, DRAM, Mobile DRAM, SDRAM, DDR/2 SDRAM, EDO/FPMS, RLDRAM, SRAM, “flash” memory (e.g., NAND/NOR), memristor memory, PSRAM, and/or other types of memory. 
     As used herein, the terms “integrated circuit”, “chip”, and “IC” are meant to refer to an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material. By way of non-limiting example, integrated circuits may include field programmable gate arrays (e.g., FPGAs), a programmable logic device (PLD), reconfigurable computer fabrics (RCFs), application-specific integrated circuits (ASICs), and/or other types of integrated circuits. 
     As used herein, the terms “microprocessor” and “digital processor” are meant generally to include digital processing devices. By way of non-limiting example, digital processing devices may include one or more of digital signal processors (DSPs), reduced instruction set computers (RISC), general-purpose (CISC) processors, microprocessors, gate arrays (e.g., field programmable gate arrays (FPGAs)), PLDs, reconfigurable computer fabrics (RCFs), array processors, secure microprocessors, application-specific integrated circuits (ASICs), and/or other digital processing devices. Such digital processors may be contained on a single unitary IC die, or distributed across multiple components. 
     As used herein, the term “network interface” refers to any signal, data, and/or software interface with a component, network, and/or process. By way of non-limiting example, a network interface may include one or more of FireWire (e.g., FW400, FW800, etc.), USB (e.g., USB2), Ethernet (e.g., 10/100, 10/100/1000 (Gigabit Ethernet), 10-Gig-E, etc.), MoCA, Coaxsys (e.g., TVnet™), radio frequency tuner (e.g., in-band or OOB, cable modem, etc.), Wi-Fi (802.11), WiMAX (802.16), PAN (e.g., 802.15), cellular (e.g., 3G, LTE/LTE-A/TD-LTE, GSM, etc.), IrDA families, and/or other network interfaces. 
     As used herein, the terms “node”, “neuron”, and “neuronal node” are meant to refer, without limitation, to a network unit (e.g., a spiking neuron and a set of synapses configured to provide input signals to the neuron) having parameters that are subject to adaptation in accordance with a model. 
     As used herein, the terms “state” and “node state” is meant generally to denote a full (or partial) set of dynamic variables used to describe node state. 
     As used herein, the term “synaptic channel”, “connection”, “link”, “transmission channel”, “delay line”, and “communications channel” include a link between any two or more entities (whether physical (wired or wireless), or logical/virtual) which enables information exchange between the entities, and may be characterized by a one or more variables affecting the information exchange. 
     As used herein, the term “Wi-Fi” includes one or more of IEEE-Std. 802.11, variants of IEEE-Std. 802.11, standards related to IEEE-Std. 802.11 (e.g., 802.11a/b/g/n/s/v), and/or other wireless standards. 
     As used herein, the term “wireless” means any wireless signal, data, communication, and/or other wireless interface. By way of non-limiting example, a wireless interface may include one or more of Wi-Fi, Bluetooth, 3G (3GPP/3GPP2), HSDPA/HSUPA, TDMA, CDMA (e.g., IS-95A, WCDMA, etc.), FHSS, DSSS, GSM, PAN/802.15, WiMAX (802.16), 802.20, narrowband/FDMA, OFDM, PCS/DCS, LTE/LTE-A/TD-LTE, analog cellular, CDPD, satellite systems, RFID or NFC, millimeter wave or microwave systems, acoustic, infrared (i.e., IrDA), and/or other wireless interfaces. 
     Overview 
     The present disclosure provides, in one aspect, apparatus and methods for implementing activity-based plasticity mechanisms configured to, inter alia, aid salient feature detection by artificial spiking neuron networks processing sensory data. 
     In some implementations, the processing may comprise determination of two or more plasticity rules based on an analysis of output of neurons encoding visual stimulus. The individual plasticity rules may be applied to one or more groups of neurons of the network. 
     In one or more implementations, the processing network may initially comprise one or more neurons that are feature agnostic (e.g., may respond to any feature within the input). During network training, different neurons may develop (emerge) preferential responses to particular features. The feature selective units may elicit strong response when they are presented with the input comprising the matching feature. By way of illustration, when processing visual scenes, red-color selective units may respond strongly when they are presented/stimulated with scenes comprising red objects. In one or more implementations, the visual scenes may correspond to traffic imagery and red objects may comprise red traffic lights. Red-selective may unit respond when they ‘see’ the red light. The red-selective unit may not respond for green light. Similarly, the orientation selective units may respond strongly when their matching orientation (e.g., vertical) is present within the input, and may respond weakly for non-matching orientation (e.g., horizontal). 
     In some implementations, unit selectivity may be aided by selective inhibition. In the above traffic processing example, two or more red (and/or green) color selective units may inhibit one another with red-to-red (and/or green-to-green) inhibitory connections. Such intra-selectivity inhibition may be referred to as the strong red-to-red/green-to-green inhibitory connections. The red color selective units may not inhibit the green color selective units. The green color selective units may not inhibit the red color selective units. Such inter-selectivity inhibition may be referred to as the weak red-to-green inhibitory connections. 
     In one or more implementations, the plasticity mechanism used in establishing the inter- and the intra-selectivity inhibition may comprise adaptive plasticity mechanism based on a similarity measure (e.g., a cross-correlogram, cross-correlation, convolution, differential entropy, and/or mutual information) between outputs of units of two or more selectivity groups (e.g., the red and the green). 
     In some implementations, as a part of network training, an output of one unit (e.g. red) may be compared to the output of other units from the same selectivity. An output of one unit (e.g. red) may be compared to (i) the output of other units from the same selectivity (e.g., other red units); and (ii) the output of units from another selectivity (e.g., green units). The adaptive plasticity rule may be constructed by determining a difference between the two similarity estimates. In some implementations, the adaptive plasticity rule may be based on averaged similarity measures. 
     The activity based adaptive plasticity rule may advantageously aid unit selectivity during network operation subsequent to training. That is, efficacy of inhibitory connections between units responding to similar features may be increased. Efficacy of inhibitory connections between units responding to different features may be reduced. As applied to the above example, inhibitory connection between red-red (green-green) units may become stronger, while inhibitory connections between red-green units may become weaker. Strong inhibitory connections between the red (and/or green) selective units, may cause red/green units to sufficiently inhibit activity (spike output generation) of one another activity. At the same time, red/green units may not inhibit sufficiently the activity of green/red units, respectively. When the input comprises a large portion of red features, the response of the red units may grow progressively weaker and/or less consistent, compared to the response of the green units. As a result, the saliency map may comprise greater emphasis at the green feature location, as illustrated in detail below. A saccade may be generated to the salient feature location. 
     In another aspect of the disclosure, adaptive adjustment methodologies are used to implement processing of visual sensory information and feature/object recognition using spiking neuronal networks. Portions of the object recognition apparatus can be embodied for example in a remote computerized apparatus (e.g., server), comprising a computer readable apparatus. 
     Embodiments of the foregoing feature detection functionality of the present disclosure are useful in a variety of applications including for instance a prosthetic device, autonomous robotic apparatus, and other electromechanical devices requiring visual or other sensory data processing functionality. 
     Methods 
     Detailed descriptions of the various embodiments and implementations of the apparatus and methods of the disclosure are now provided. Although certain aspects of the disclosure can best be understood in the context of processing visual information using spiking neural networks, the disclosure is not so limited, and implementations of the disclosure may also be used in a wide variety of other signal processing applications, including for instance in processing of other sensory signal modalities (e.g., sound waves, radio frequency waves, etc.) and/or implementing connection adaptation in pulse-code neural networks. 
     Implementations of the disclosure may be for example deployed in a hardware and/or software realization of a neuromorphic computer system. In one such implementation, a robotic system may include a processor embodied in an application specific integrated circuit, which can be adapted or configured for use in an embedded application (such as a prosthetic device). 
       FIG. 2  illustrates one implementation of an image processing apparatus comprising an activity-based salience map generation methodology of the present disclosure. An area  204  within the visual scene  202  may comprise a salient feature  216  (denoted as ‘X’ in  FIG. 2 ). The area  204  may correspond to an aperture of a lens, an imaging sensor array (comprising RGCs, a charge coupled device (CCD) or CMOS device, or an active-pixel sensor (APS)), an optic of an eye, etc. The area  204  may be referred to as an image. The image  204  may be projected (interfaced) to encoder  206 . In some implementations, the encoder may comprise spiking retina encoder described, for example, in co-owned and co-pending U.S. patent application Ser. No. 13/539,142, “RETINAL APPARATUS AND METHODS”, filed Jun. 29, 2012, U.S. patent application Ser. No. 13/623,820, entitled “APPARATUS AND METHODS FOR ENCODING OF SENSORY DATA USING ARTIFICIAL SPIKING NEURONS”, filed Sep. 20, 2012, or U.S. patent application Ser. No. 13/623,838, entitled “SPIKING NEURON NETWORK APPARATUS AND METHODS FOR ENCODING OF SENSORY DATA”, filed, Sep. 20, 2012, each incorporated herein by reference in its entirety. The encoder  206  may convert the image data  204  into spike output using, for example, latency encoding described in U.S. patent application Ser. No. 13/548,071, entitled “SPIKING NEURON NETWORK SENSORY PROCESSING APPARATUS AND METHODS”, filed Jul. 12, 2012, incorporated herein by reference in its entirety. In one or more implementations, the encoder  206  may convert the image data  204  into spike output using, for example, spike rate encoding, and/or spike polychronous patterns as described, for example, in U.S. patent application Ser. No. 13/117,048, entitled “APPARATUS AND METHODS FOR POLYCHRONOUS ENCODING AND MULTIPLEXING IN NEURONAL PROSTHETIC DEVICES”, filed May 26, 2012, incorporated herein by reference in its entirety. 
     The encoded image data may be coupled form the encoder  206  to image processing and/or feature detection block  210  via one or more fee-forward connections  209 . The processing block  210  may comprise one or more spiking neurons  208 _ 1 ,  208 _ 2 . The connections  209  may be characterized by a connection efficacy. Efficacy refers in one implementation to a magnitude and/or probability of input spike influence on neuronal response (i.e., output spike generation or firing). Efficacy may comprise, for example a parameter (e.g., synaptic weight, probability of transmission, and/or other parameter) by which one or more state variables of the neurons  208  may be changed. 
     Connection efficacy may be changed in accordance with one or more STDP rules. In some implementations, individual connections may utilize connection-specific rules. Different classes of connections (e.g., feed-forward, lateral, and/or feedback) may in one implementation utilize type-specific common STDP rules. 
     In some implementations, the STDP rule may comprise an adaptive STDP mechanism that may be determined in real time by a network entity and/or another entity as described, for example, in U.S. patent application Ser. No. 13/660,923, entitled “MODULATED PLASTICITY APPARATUS AND METHODS FOR SPIKING NEURON NETWORK”, incorporated supra. 
     The neurons  208  may be configured to respond preferentially to one or more features within the image  204 . In some implementations, the first neuron  208 _ 1  may be configured, for example, to respond to the feature  216 , while the second neuron  208 _ 2  may be configured, to respond to a feature other than ‘X’ in  FIG. 2 . Such neurons,  201 _ 1 ,  208 _ 2  may be referred to as the neurons of different class (e.g., responding to different feature set). Neurons  208  may further be configured to inhibit one another via the inhibitory contention  212 . The connections  212  may be characterized by a connection efficacy of the type previously described. 
     The processing block  210  may detect the salient feature  216  in the image  204 . In some implementations, the block  210  may communicate a saliency map (comprising, for example coordinates of the salient feature  216 ) to the saccading block  218  via the connections  214 . In some implementations, the feature coordinates may be determined based on the spatial position of the neurons that may respond to the feature. By way of a non-limiting example, the neurons  208 _ 1 ,  208 _ 2  may be spatially arranged and the connections to the saccading block may comprise a topographic coordinate parameter. In some implementations, the block  218  may accumulate information from other parts of the visual field (e.g., other neurons of the processing block  210 ). The block  218  may further process information related to spatial position features within the visual field  204  that cause activity of the neurons of the block  210 . In one or more implementations, the block  218  may produce a saliency map that may be used to determine the saccading location (e.g., the field  224 ) within the scene  202 . 
     The block  218  may generate one or more commands in order to saccade the aperture to the location of the salient feature  216 , thereby causing the image  224  to be acquired. In one or more implementations, the saccading block may comprise one or more actuators configured to reposition, for example, the imager lens so that the salient feature is in the center of the aperture (e.g., the image  224 ). In some implementations (not shown), the saccading block  218  may be embedded within the image processing block  210 . 
       FIG. 3  illustrates exemplary salient feature types useful with the image processing apparatus  200  of  FIG. 2 . The salient feature (e.g., the feature  216  of  FIG. 2 ) may comprise one or more characteristics that make it distinct from the background and/or other features. Such characteristics may include of example luminance (e.g., a single darker circle  306  relative other circles in the panel  300 ); color: (e.g., a single white circle  316  among black circles in the panel  310 ); motion: e.g., a single mobbing circle  326  relative stationary circles in the panel  320 ); and/or orientation (e.g., a single horizontal bar  336  among vertical bars in the panel  330 ). It will be recognized by those skilled in the arts that many other object characteristics may be equally compatible and useful with the disclosure, for example, polarization, texture, and/or others). 
       FIG. 4A  illustrates one exemplary implementation of a spiking neuronal network of the image processing block  210  of  FIG. 2 . The network  400  may comprise one or more units (e.g., spiking neurons)  410 . The units  410  may be configured to receive feed-forward spiking input  406  (e.g., the input  209  in  FIG. 2 ) via one or more connections  404 . In some implementations, the neuron (e.g., the neuron  410 _ 1 ) may receive inhibitory input  419  from another neuron (e.g.,  410 _ 2  in  FIG. 4A ) via one or more inhibitory connections  418 . In some implementations (not shown), the first neuron  410 _ 1  may provide an inhibitory signal to the second neuron  410 _ 2 , thereby effectuating mutual inhibition. The inhibitory connection  418  may be characterized by an efficacy, depicted by the solid circle  409  in  FIG. 4A . 
     In one or more implementations, the inhibition may be configured to directly affect neuron excitability. By a way of a non-limiting example, the neuron excitability may be reduced proportional to the magnitude of the value of inhibition signal. 
     In some implementations, the inhibition may be utilized as a gating parameter affecting output spike generation by the neuron. Spike generation by a neuron may be based on, for instance, a parameter E describing strength of excitatory input into the neuron (e.g., by the feed-forward input  406  in  FIG. 4A ). By a way of a non-limiting example, a strong input excitation may correspond to E&gt;=2; moderate excitation may correspond to 2&gt;E≧1; and weak excitation correspond to E&lt;1. In some implementations, in absence of other inputs, strong excitation may be characterized by a high probability of neuronal response (e.g., P&gt;0.9); weak excitation may correspond to a low probability of neuronal response (e.g., P&lt;0.1) and moderate excitation correspond to probability of neuronal response of e.g., about 0.5. As will be appreciated by those skilled in the arts, the above numbers comprise one or more exemplary implementations, and other probability ranges may be utilized so long that strong excitation corresponds to higher response probability compared to moderate excitation, and weak excitation corresponds to lower response probability compared to moderate excitation. 
     In some implementations, efficacy of the inhibitory connections (e.g., the connection  418  in  FIG. 4A ) may be characterized by an inhibitory parameter B. In one or more implementations, strong inhibition may correspond to B≧1; while weak inhibition may correspond to B&lt;0.1. Strong inhibition may be sufficient to suppress neuron response even when excitatory input is strong. Weak inhibition may not be sufficient to suppress neuron response due to strong and/or moderate excitatory input (e.g., E≧1). Weak inhibition may suppress neuron response due to weak excitatory input (e.g., E&lt;1). In some implementations, neuron response suppression may be characterized by P=0 (no response altogether); while in some implementations the suppressed neuron may respond with a low probability (albeit non-zero, such as e.g., P˜0.01). 
     The strength of the neural response may be configured based for instance on the strength of the excitatory input, and/or on the strength of the inhibitory input. In some implementations, the strength of the neural response may be characterized by the latency of the output spike referenced to a time base. The time base may comprise an input time (e.g., video frame time). In some implementations, the time base may comprise a timer event, and/or other signal. In one or more implementations, the strength of the neural response may be characterized by the number of spikes emitted by the neuron in a short time window (e.g. 100 ms) after the arrival of the input. By a way of a non-limiting example, a strong excitatory input may trigger the neuron to generate one (or more) spikes, where the first spike may be characterized by a latency L1 relative to the arrival of the input to the neuron. A weaker input may trigger one spike with a latency L2 that is substantially longer, as compared to the L1 latency. In some implementations, the L1 value may be selected at 1 ms (or shorter). The L2 value may be configured to be greater than or equal to about 100 ms. 
     The neurons  410  may generate output (e.g., a spike) using any of a number of possible methodologies, such as for example those described in co-owned and co-pending U.S. patent application Ser. No. 13/152,105 filed on Jun. 2, 2011, and entitled “APPARATUS AND METHODS FOR TEMPORALLY PROXIMATE OBJECT RECOGNITION”, co-owned and co-pending U.S. patent application Ser. No. 13/152,119 filed on Jun. 2, 2011, and entitled “SENSORY INPUT PROCESSING APPARATUS AND METHODS”, each of the foregoing incorporated herein by reference in its entirety. In one or more implementations, the neuron spike generation mechanism may comprise input scaling and/or firing threshold adjustment, as described for example in U.S. patent application Ser. No. 13/623,820, entitled “APPARATUS AND METHODS FOR ENCODING OF SENSORY DATA USING ARTIFICIAL SPIKING NEURONS”, incorporated supra. The spikes of the neuron  410  may be propagated via the connection  414 . 
     Connections  404  may be characterized by a connection efficacy, depicted by open circles  408  in  FIG. 4A . Connection efficacy may be adjusted in accordance with, e.g., a plasticity mechanism. In one or more implementations, the plasticity mechanism may be adaptively configured based on a similarity measure (between neuron output (e.g., the output  416 ) and the neuron input (e.g., the input  406 _ 1 ,  406 _ 2 ,  419  in  FIG. 4A ), as described in detail in U.S. patent application Ser. No. 13/660,923, entitled “ADAPTIVE PLASTICITY Apparatus and Methods FOR Spiking Neuron Network”, incorporated supra. In one or more implementations, the similarity measure may be based on one or more of a cross-correlogram measure and/or mutual information measure. 
       FIG. 4B  illustrates unit specificity attainment and plasticity development by the encoder  210  of  FIG. 2  during training, according to one or more implementations. The panel  450  in  FIG. 4B  illustrates an operational timeline of the network  420 . 
     In one or more implementations, at time t0, the processing network (e.g., the network  400  of  FIG. 4A , and/or network  420  of  FIG. 4B ) may initially comprise one or more neurons  411  (e.g., the neurons  410  of  FIG. 4A ) that are feature-agnostic (e.g., may respond to any feature within the input). The neurons  411  of the network  420  may be interconnected by a plurality of connections  412 . The connections  412  may be configured to provide one-way or mutual lateral inhibition between neurons  411 . In some implementations, the connectivity between the neurons may be all-all (i.e., individual neuron may be connected to all neurons of at least a portion of the network). In one or more implementations, the network portion may be selected based on a spatial parameter, such as a coordinate described in detail in U.S. patent application Ser. No. 13/385,938 entitled “TAG-BASED APPARATUS AND METHODS FOR NEURAL NETWORKS” filed on Mar. 15, 2012, incorporated herein in its entirety. In some implementations, other connectivity patterns may be employed, such as, for example, one-to-one, one to-many, one-to-all, subset-to subset, and/or other patterns. 
     During network training, different neurons may develop (emerge) preferential responses to particular features, as illustrated by the networks  422 ,  430  in  FIG. 4B . Based on the feed-forward input comprising one or more frames  452  (e.g., the input  209  in  FIG. 2 ) at time t1, one or more of the circle units  411  may learn to respond to, for example, horizontal features in the input image frame (e.g., as in the frame  600  in  FIG. 6A ). Such horizontal-specific units are depicted by the squares  432 _ 1 ,  432 _ 2  in  FIG. 4B ), and may be referred to as the ‘squares’. Similarly, one or more of the circle units  411  may learn to respond to, for example, vertical orientation in the input image. Such vertical-specific units are depicted by the triangles  434  in  FIG. 4B , may be referred to as the ‘triangles’. In some implementations, one or more circles (e.g., configured to respond to a slanted feature) may remain unspecific due to, for example, insufficient (and/or absent) slanted stimulus in the input frames  452 . The circle units may generate output  446  in  FIG. 4B . 
     The feature selective units (e.g., the squares  432 , and/or the triangles  434 ) may elicit strong response when they are presented with the input comprising the matching feature. In some implementations, unit selectivity may be aided by selective inhibition. As the network (e.g., the network  420  of  FIG. 4B ) develops feature specificity, it may comprise the network  422  of feature-specific units. 
     The feature selectivity of the network  422  may be based, at least partly, on a differentiation between the intra-unit inhibitory connections  426 ,  428  and inter-unit connections,  429 . The connection may develop during learning so that a portion of the original lateral connections  412  of the network  420  may be transformed into the inter-unit connections. Another portion of the original lateral connections  412  of the network  420  may be transformed into the intra-unit connections. 
     Two or more square units  432  (and/or triangle units  434 ) may inhibit one another with square-to-square (and/or triangle-to-triangle) inhibitory connections  426 ,  428 , respectively in  FIG. 4B , as described in detail with respect to  FIG. 6A , below. Such inhibitory connections  426 ,  428  may be referred to as “strong intra-selectivity inhibition”, and are depicted with thick lines denoted by the sign ‘+’ in  FIG. 4B . 
     The vertically selective units (e.g., the triangles in  FIG. 4B ) may provide weaker inhibition to the horizontally selective units (e.g., the squares in  FIG. 4B ). Similarly, the horizontally selective units may provide weaker inhibition to the vertically selective units. Such inhibitory connections  429  in  FIG. 4B  may be referred to as “weak inter-selectivity inhibition”, and are depicted with thin lines denoted by the sign ‘−’ in  FIG. 4B . 
     In some implementations, the square (and/or the triangle) units may not inhibit one another when the efficacy of the triangle-to-square and square-to-triangle synapses  429  in  FIG. 4B  is not sufficiently high to cause inhibition. In one or more implementations, the square (and/or the triangle) units may weakly inhibit one another. 
     In one or more implementations, the output  442  of the squares and/or  444  of triangles may be used to derive an inhibitory plasticity mechanism for use with the connections  426 ,  428 ,  429 . In some implementations, the output  442 _ 1  of one square may be compared with the output of one or more other squares (e.g., the output  442 _ 2 ), as illustrated by the inter-selectivity operator  454  in  FIG. 4B . In some implementations, the output  442 _ 1  of one square may be compared with the output of one or more triangles (e.g., the output  444 ), as illustrated by the intra-selectivity operators  452 _ 1 ,  452 _ 2  in  FIG. 4B . In some implementations, the output  444  of one triangle may be compared with the output of one or more squares (e.g., the output  442 _ 1 ,  442 _ 2 ). 
     In some implementations, output comparison between all available square-to-square pair combinations may be computed. In one or more implementations, outputs of a subset of the square unit population may be evaluated. The subset may be for example randomly selected, or selected according to other criteria. In one or more implementations, the output record may comprise the whole learning window  454 , or a portion thereof. 
     In one or more implementations, the plasticity mechanism used in establishing inter- and intra-selectivity inhibition may be comprise an adaptive plasticity mechanism based on the output activity comparison (e.g., the output of the operators  452 ,  454 ); e.g., determining a similarity measure C. In some implementations, the similarity measure may comprise one or more of a cross-correlogram, cross-correlation, convolution, differential entropy, and/or mutual information between the outputs  422 ,  444 . 
       FIG. 12  illustrates one implementation of such an adaptive mechanism. When the neuron generates an output (fires a spike  442 _ 1  in  FIG. 4B , and/or spike  1202  in  FIG. 12 ) at time t post , the cross-correlogram may be determined based on (i) a time record of post-synaptic response of another neuron (e.g., the output  442 _ 2 , in  FIG. 4B , and/or output  1210  in  FIG. 12 ) during a time interval t post   1 −ΔT; and (ii) a time record of post-synaptic output (e.g., the output  1200  in  FIG. 12 ) by the neuron within the same time interval ΔT  1224 . In some implementations for processing of visual input refreshed at 40 ms intervals (25 frames per second), the time interval ΔT may be selected, from the range between 1 and 1000 ms, preferably 40 ms. It will be appreciated by those skilled in the arts, that the interval ΔT may be adjusted in accordance with the temporal characteristics of the input. In some implementations adapted to process, for example, high-speed imagery, the plasticity interval may be shortened. In implementations adapted to process, for example, medical ultrasonograms and/or seismic imagery, the plasticity interval may be increased. 
     In one or more implementations, multiple correlogram estimates (associates with multiple post-synaptic responses  1202 ) may be averaged to produce a time-averaged similarity measure  1220 . In some implementations, the average histogram  1220  maybe computed by averaging over the last 1000 spikes across all input synapses or may be computed by averaging over the last 100 second time period. In one or more implementations (not shown), the averaged similarity measure may be determined by e.g., averaging similarity measures of two or more neuron pairs (e.g., the neurons  432 ,  434  in  FIG. 4B ). 
     In some implementations, individual spikes (e.g., the spike groups  1200 ,  1210  in  FIG. 12 ) may be assigned the same amplitude (e.g., binary 1). Accordingly, the binary correlogram  1220  may be interpreted as a histogram of other neuron activity within individual time slots (bins)  1222  prior to the response of the neuron. In some implementations, the time step (bin width)  1222  may be selected equal to 1 ms. The contents of bins that correspond to one or more activity pulses (e.g., the spikes  1210  in  FIG. 12 ) may be incremented, as depicted by the hashed bins (e.g., the bin  1228 ) in  FIG. 12 . 
     An averaged similarity measure (e.g., the correlogram  1220 ) may be used to construct plasticity rules for the connections of the neuron, as described in detail below with respect to  FIG. 5 . 
     Returning now to  FIG. 12 , when the neuron (e.g., the neuron associated with the trace  1202  post_ 1 ) generates post-synaptic response ( 1230  in  FIG. 12 ), the history of activity of other neurons may be evaluated. One or more activity pulses (the spikes  1232 ,  1234 ,  1236 ) may be identified within the time window ΔT, prior to the neuron response spike  1230 . Plasticity components (e.g., the components  1242 ,  1244 ,  1246 ), corresponding to the activity times t post     —     n   i  of the identified pulses  1232 ,  1234 ,  1236 , may be combined by an operator  1240  to produce efficacy adjustment w  1248 . In some implementations, the adjustment may be performed based on an event, such as timer expiration, buffer overflow, external (reward) indication, and/or other event types). 
       FIG. 5  presents performance results obtained during simulation and testing by the Assignee hereof, of exemplary computerized spiking network apparatus configured to implement image processing framework (described above with respect to  FIGS. 2-4B ). The curve  502  in  FIG. 5  denotes the intra-selectivity similarity measure based on cross-correlation between output spikes of units responding to two horizontally oriented features. The curve  504  in  FIG. 5  denotes the inter-selectivity output comparison based on cross-correlation between output spikes of one unit responding to horizontally oriented features, and a unit responding to vertically oriented features. In one implementation, the similarity measure (such as cross-correlation  502 ,  504 )) may be determined over a longer time-period. In some implementations, the time period may be selected between several seconds to several hours of network operation time. The data used for determining the curves  502 ,  504  correspond to 200 seconds of network operation processing input frame stream at 25 frames per second. The curves  502 ,  504  comprise an average of two individual unit-unit estimates. 
     The adaptive plasticity for use with inhibitory lateral connections (e.g., the connections  426 ,  428 ,  429  of the network  422  of  FIG. 4B ) may be constructed based on a difference between the inter-selectivity similarity measure (e.g., the curve  502  in  FIG. 5 ) and the intra-selectivity similarity estimate (e.g., the curve  504  in  FIG. 5 ). The curve  506  is based on the difference between the curve  502  and  504 , respectively. 
     In some implementations, the adaptive plasticity rule may be based on averaged similarity measures. In some implementations, the plasticity rule R1 (e.g., the curve  506  in  FIG. 5 ) may be determined based on a difference of (i) similarity measure C1 between the output activity of horizontal and horizontal selective units; and (ii) similarity measure C2 between the output activity of horizontal and vertical selective units. In one or more implementations, the plasticity rule R2 may be determined based on a difference of (i) similarity measure C3 between the output activity of vertical and vertical selective units; and (ii) similarity measure C2 between the output activity of horizontal and vertical selective units. In some implementations, the overall plasticity rule may be based on a combination of R1 and R2:
 
 R=aR 1 +bR 2.  (Eqn. 1)
 
where a,b are the combination weights.
 
     The resulting curve  506  in  FIG. 5  illustrates the plasticity rule comprising a long term potentiation (LTP) window  508 , and a long term depression (LTD) window  510 . The x-axis describes the time delay Δt=t post −t pre , where t pre  corresponds to the time of the arrival of the pre-synaptic spike to the post-synaptic unit (e.g., the spike  419  on the connection  418  in  FIG. 4A ); and t post  corresponds to the time of neuron response (e.g., the spike  416  in  FIG. 4B ). As seen from the curve  502 , the intra-selectivity activity (e.g., horizontal-horizontal) occurs substantially contemporaneously with one another, more frequently within the time interval approximately coinciding with the LTP window  506 . According to the plasticity curve  506 , horizontal-to-horizontal unit connections may be strongly potentiated. 
     The curve  502  of  FIG. 5  describes intra-selectivity activity distribution for Δt=t post −t pre . When the plasticity curve  506  is sampled using the  502  distribution, the efficacy of the intra-feature connections (such as  426 ,  428  in  FIG. 4B ) is more likely to be potentiated (using the portion  508  of the curve  506 ) than depressed when averaged over time. In other words, when the plasticity rule is applied over a period of time, the time-averaged probability of the connection being potentiated is greater than being depressed. 
     Similarly, the curve  504  in  FIG. 5  describes the inter-selectivity activity distribution for Δt=t post −t pre . When sampling the plasticity curve  506  with the  504  distribution, the efficacy of the inter-feature connections (such as  429  in  FIG. 4B ) is more likely to be depressed (using the portion  510  of the curve  506 ) rather than potentiated when averaged over a time interval. 
     In some implementations, the averaging interval may be selected as e.g., 1000 seconds or longer. 
     Applying the STDP mechanism with the plasticity curve  506 , the efficacy of the intra-feature connections may become potentiated (i.e., producing a “strong connection”), and the efficacy of the inter-feature connections may become depressed (i.e., producing a weak connection). In some implementations, a ratio of the “strong connection” efficacy to the “weak connection” efficacy may be a factor of 3 or greater. 
     As seen from the curve  504 , Δt=t post −t pre  for the inter-selectivity activity (e.g., horizontal-vertical) is more widely distributed, with a portion of activity occurring substantially in the interval  508  and a portion of activity occurring substantially in the interval  510 . The broader interval  510  (compared to the interval  508 ) approximately coincides with the LTD portion of the rule  506 . According to the plasticity curve  506 : (i) at least a portion of the horizontal-to-vertical unit connections may be depressed compared to the horizontal-to-horizontal connections; and (ii) at least a portion of the horizontal-to-vertical unit connections may be depressed. In some implementations, the plasticity mechanism may adjust the efficacy of synapses based, for example, on the curve  506  of  FIG. 5 , and the time intervals Δt between post-synaptic responses and pre-synaptic spikes. The efficacy adjustment of, for example, the curve  506  may increase connection efficacy (potentiate the connection) when the time intervals Δt fall within the interval range  508 . Conversely, the rule of the curve  506  may decrease connection efficacy (depress the connection) when the time intervals Δt fall outside the interval range  508 , e.g., within the interval range  510 . 
     In one or more implementations, the plasticity rule based for example on the curve  506 , may cause depression of the horizontal-to-vertical neuron connections, when the plasticity rule is applied for a lengthier period (e.g., 1000 (or more) seconds). The plasticity rule based on the curve  506  may cause connection potentiation when the plasticity rule is applied for about 1000 seconds. In some implementations, the connection plasticity may be effectuated for periods in excess of 1000 s. 
     The dynamic state of the neuron units (e.g., the units  411  in  FIG. 4B ) may also be periodically updated. In some implementations, the update may comprise a cyclic update effectuated at regular intervals (e.g., 1 ms) as described in detail, for example, in U.S. patent application Ser. No. 13/560,891, entitled “APPARATUS AND METHODS FOR EFFICIENT UPDATES SPIKING NEURON NETWORKS”, filed on Jul. 27, 2012, incorporated herein by reference in its entirety. In one or more implementations, the update may be based on the neuron post-synaptic response, as described in detail in U.S. patent application Ser. No. 13/239,259, entitled “APPARATUS AND METHOD FOR PARTIAL EVALUATION OF SYNAPTIC UPDATES BASED ON SYSTEM EVENTS”, incorporated herein by reference in its entirety. 
       FIG. 6A  illustrates one implementation of salient feature detection (also referred to as the “pop-up emergence”) comprising an adaptive activity-based plasticity mechanism described above with respect to  FIGS. 4A-5 . The panel  600  illustrates the input image (e.g., the image  204 ) comprising a horizontally oriented feature  604  and several vertically oriented features  606 . The image  600  may be provided to a spiking neuron network processing apparatus (e.g., the apparatus  200  of  FIG. 2 ). 
     The panel  610  illustrates a spiking neuron network comprising two (or more, not shown) spiking neurons  612 ,  614  that may develop receptive field such that to respond to vertical and horizontal features within the image  600 , respectively. The spiking neuron network  610  may be operable in accordance with the activity based inhibition mechanism comprising:
         the intra-selectivity connections (e.g.,  616 ,  618  in  FIG. 6 ) that may provide strong inhibition to units of the same selectivity; and   the inter-selectivity connections (e.g.,  620  in  FIG. 6 ) that may provide weaker (compared to the connections  616 ,  618 ) inhibition to units of different selectivity.       

     The spiking neuron network  610  may be operable in accordance with the activity based inhibition mechanism:
         the intra-selectivity connections (e.g.,  616 ,  618  in  FIG. 6 ) may provide strong inhibition to units of the same selectivity; and   the inter-selectivity connections (e.g.,  620  in  FIG. 6 ) may provide weaker (compared to the connections  616 ,  618 ) inhibition to units of different selectivity.       

     In one or more implementations, the connections  616 ,  618 ,  620  may provide inhibitory input to the units  612 ,  614 . Inhibitory input may be configured to reduce unit excitability and/or move the unit further away from the response-generating state. Unit-to-unit inhibition may be based on an early responding unit inhibiting later responding units, such as using a temporal “winner takes all” methodology described in detail in for example, U.S. patent application Ser. No. 13/548,071, entitled “SPIKING NEURON NETWORK SENSORY PROCESSING APPARATUS AND METHODS”, filed Jul. 12, 2012, incorporated supra. When the connections  616 ,  618  are potentiated, a probability of the units  612 ,  614 , respectively, to generate output spikes may be reduced and/or suppressed altogether. As the frame  600  comprises many more vertically oriented features, activity of the units  612  (e.g., squares) selective to the vertical features may be lower compared to the activity of units  614  responding to horizontally oriented features (e.g., the triangles). Strong inhibitory connections  626  between square units of the network  630  in  FIG. 6  may cause inhibition of a large portion (or all) of the square units. 
     While the number of (strong) inhibitory connections  618  between the triangles  614  may be the similar (or same) at the number of (strong) inhibitory connections  616  between the squares  612 , because the input  600  contains fewer vertical features  604 , there may be fewer active square units (e.g., the units  612  responding to the feed-forward input). Based on a lower (compared to the input associated with the horizontal features  606 ) amount of vertical features  604  in the image  600 , a fewer number of triangle units may receive strong feed-forward input associated with the vertical features, therefore individual square unit  612  (responding to vertical features) may receive less inhibition from the square-to-square inhibitory connections  616  in  FIG. 6A . 
     The triangle units  614  of  FIG. 6A  may be strongly activated by the feed-forward input associated with the horizontal features  606 . The triangle units  614  may strongly inhibit each other via the triangle-to-triangle inhibitory connections  618 . 
     Weaker inhibitory connections  620  between the square units  612  and the triangle units  614  may cause lower inhibition of the triangle units. The network  610  plasticity configuration may increase probability of the network selectively responding to the salient vertical feature  604 , as illustrated by the emergence of the pop-out, as shown in  FIG. 6B . 
       FIG. 6B  depicts a saliency map  640  comprising the salient area (the pop-out)  642 . Spatial location (X,Y) of the pop-out  642  approximately corresponds to the location of the vertical feature  604  in the input image  600  of  FIG. 6A . Comparison of the saliency map  640  obtained using the adaptive plasticity methodology of the present disclosure to a saliency map of the prior art  650  in  FIG. 6B , clearly illustrates that the adaptive plasticity methodology of the disclosure is capable of unambiguously isolate the location of the salient feature  604  in the input image  610 . 
     In some implementations, the map  640  may be communicated to an image acquisition block (e.g., the saccading block  216  of  FIG. 2 ) in order to, for example, position a center of the field of view (imaging array aperture) at the salient feature. 
     Referring now to  FIGS. 7-9 , exemplary implementations of adaptive plasticity methods according to the disclosure are described. In some implementations, the methods of  FIGS. 7-9  may be used, for example, for operating the neurons  410  of  FIG. 4A . Methods of  FIGS. 7-9  may be implemented in a connection (e.g., the connection  418  of  FIG. 4A ). The methods of  FIG. 7-9  may also be implemented in a sensory processing apparatus, comprising one or more spiking neuron networks as described with respect to  FIG. 10 , infra, thereby advantageously aiding, inter alia, accurate and/or timely saccading. 
       FIG. 7  illustrates a method of determining adaptive plasticity for a spiking neuron based on a similarity measure between neuron input and output, in accordance with one implementation. 
     At step  702  of method  700 , an input image may be accessed. In some implementations, image may comprise a plurality of pixels generated by an imaging array (comprising RGCs, a charge coupled device (CCD), or an active-pixel sensor (APS)). In one or more implementations, the image may comprise a light output of an optic of an eye. 
     At step  704  of the method  700 , the image may be encoded into spikes. In some implementations, the encoding may comprise latency encoding described in U.S. patent application Ser. No. 13/548,071, entitled “SPIKING NEURON NETWORK SENSORY PROCESSING APPARATUS AND METHODS”, filed Jul. 12, 2012, incorporated supra. In one or more implementations, the image data may be converted to spike output using, for example, spike rate encoding, and/or spike polychronous patterns as described, for example, in U.S. patent application Ser. No. 13/117,048, entitled “APPARATUS AND METHODS FOR POLYCHRONOUS ENCODING AND MULTIPLEXING IN NEURONAL PROSTHETIC DEVICES”, filed May 26, 2012, incorporated herein by reference in its entirety. 
     At step  706 , a saliency map associated with et encoded spike output may be generated using activity based plasticity mechanism, such as described above with respect to  FIGS. 4A-6 . 
     At step  708 , the saliency map may be communicated to image acquisition block (e.g., the saccading engine  216  of  FIG. 2 ). The saliency map may be utilized by the image acquisition block to reposition imaging aperture in accordance with the location of salient features. 
       FIG. 8  illustrates one exemplary method of determining activity based plasticity useful, for example, with the method  700  of  FIG. 7 . 
     At step  812  of method  810 , an interval for determining activity based plasticity rule may be established. In some implementations, the similarity determination interval may be based on a historical record of spiking neuron activity when processing visual input. The time interval may be selected between several seconds and several hours. 
     At step  814 , neuron activity history associated with the interval may be accessed. In one or more implementations, the activity history may be stored by individual neurons and/or connections (e.g., memory block  1134  of  FIG. 11C )). In one or more implementations, the activity history may be stored in a memory buffer shared by one or more neurons and/or connections (e.g., the memory  1108  of  FIG. 11A ). In one or more implementations, the neuron activity may comprise activity of two or more neuron types configured to respond to different input features (e.g., vertical  1  and horizontal features). 
     At step  816 , a similarity measure C1i(Xi,Xj) between the output of the units of the same type (e.g., horizontally selective units) may be determined. 
     At step  818 , a similarity measure C2i(Xi,Yi) between the output of the units of the different types (e.g., horizontally and vertically selective units) may be determined. In some implementations, the similarity measures C1i, C2i may be based on correlogram, and/or cross correlation between the unit outputs (Xi, Xi) and/or (Xi, Yi). In one or more implementations, the similarity measure may be based on mutual information determined as follows: 
                       I   ⁡     (     X   ;   Y     )       =       ∑     y   ∈   Y       ⁢       ∑     x   ∈   X       ⁢       p   ⁡     (     x   ,   y     )       ⁢     log   ⁡     (       p   ⁡     (     x   ,   y     )           p   ⁡     (   x   )       ⁢     p   ⁡     (   y   )           )               ,           (     Eqn   .           ⁢   2     )               
where:
 
     p(x,y) is the joint probability distribution function of X and Y; and 
     p(x) and p(y) are the marginal probability distribution functions of X and Y respectively. 
     In some implementations, the similarity measures C1i, and/or C2i may be determined for one or more respective unit pairs (Xi, Xi), (Xi, Yi). An averaged similarity measure may be determined as a weighted average:
 
   C     =Σ   i=1   N ( a   i   C   i )+ a   0     C 1 =Σ i=1   N ( a   i   C 1 i )   C     =Σ   i=1   N ( a   i   C   i )  (Eqn. 3)
 
where a i  comprise the weights, and a 0  is a biasing term.
 
     At step  820 , plasticity rule may be configured based on a difference of the two similarity measures C1, C1. In some implementations, the plasticity rule determination may comprise approach described with respect to  FIG. 5 , supra. 
     In some implementations, the method  800  may be performed once, after the different neurons developed (emerged) preferential responses to particular features, as illustrated by the networks  420 ,  422 ,  430  in  FIG. 4B . 
     The method  800  may also be implemented iteratively. 
     In one or more implementations comprising cyclic updates of the network, the method  800  may be configured to be evaluated at every step (e.g., update) of the network operation. That is, the similarity measures and the plasticity rule may be continuously determined and/or refined. 
       FIG. 9  illustrates a method of updating activity-based plasticity rule (obtained for example using the method  810  of  FIG. 8 , in accordance with one implementation. 
     At step  932  of the method  930 , connection update may be performed. In some implementations, the update may be based on the adaptively derived activity based plasticity rule (e.g., the rule  506  of  FIG. 5 ). 
     At step  934 , a check may be performed whether the plasticity rule (e.g., used in the update of the step  932 ) is to be updated. 
     If the rule to be updated, the method may proceed to step  936 , where recent activity of the units may be accessed. In some implementations, the recent activity may comprise activity within a pre-determined interval (e.g., the interval  546  of  FIG. 4B ). In one or more implementations, the recent activity may comprise activity since most recent rule determination and/or update. 
     At step  938 , a plasticity rule may be determined based on the recent activity. In some implementations, the plasticity rule r may be determined in accordance with the methodology of the method  810  described above with respect to  FIG. 8 . In one or more implementations, the plasticity rule r may be determined using a difference of similarity measures between: (i) units of the same specificity; and (ii) units of different specificities. 
     At step  940 , the updated plasticity rule R′ used for connection updates (e.g., the updates of step  932  of method  930 ) may be obtained as:
 
 R′=aR+br   (Eqn. 4)
 
where:
 
     R is the previous rule; and 
     r is the rule based on the recent activity; and 
     a,b are combination weights. 
     In some implementations, the updated rule R′ may be based on the most recent data (a=0 in Eqn. 4). In some implementations, the updated rule R′ may comprise an exponential filter (b=1−a in Eqn. 4). 
     Exemplary Apparatus 
     One exemplary spiking neuron network apparatus for processing of sensory information (e.g., visual, audio, somatosensory) useful in an autonomous robotic device, is shown in  FIG. 10 . The illustrated processing apparatus  1000  may comprise an input interface configured to receive an input sensory signal  1020 . In some implementations, this sensory input comprises electromagnetic waves (e.g., visible light, IR, UV, and/or other electromagnetic wages) entering an imaging sensor array (comprising RGCs, a charge coupled device (CCD) or CMOS device, or an active-pixel sensor (APS)). The input signal in this case is a sequence of images (image frames) received from a CCD camera via a receiver apparatus, or downloaded from a file. The image may be a two-dimensional matrix of RGB values refreshed at a 24 Hz frame rate. It will be appreciated by those skilled in the art that the above image parameters are merely exemplary, and many other image representations (e.g., bitmap, CMYK, grayscale, and/or other image representations) and/or frame rates are equally useful with the present invention. 
     The apparatus  1000  may comprise an encoder  1024  configured to transform (encodes) the input signal into an encoded signal  1026 . In some implementations, the encoded signal comprises a plurality of pulses (also referred to as a group of pulses) configured to model neuron behavior. The encoded signal  1026  may be communicated from the encoder  1024  via multiple connections (also referred to as transmission channels, communication channels, or synaptic connections)  1004  to one or more neuronal nodes (also referred to as the detectors)  1002 . 
     In the implementation of  FIG. 10 , different detectors of the same hierarchical layer may be denoted by an “_n” designator, such that e.g., the designator  1002 _ 1  denotes the first detector of the layer  1002 . Although only two detectors ( 1002 _ 1 ,  1002   —   n ) are shown in the implementation of  FIG. 10  for clarity, it is appreciated that the encoder can be coupled to any number of detector nodes that is compatible with the detection apparatus hardware and software limitations. A single detector node may be coupled to any practical number of encoders. 
     In some implementations, individual ones of the detectors  1002 _ 1 ,  1002   —   n  may contain logic (which may be implemented as a software code, hardware logic, or a combination of thereof) configured to recognize a predetermined pattern of pulses in the encoded signal  1004 , using for example any of the mechanisms described in U.S. patent application Ser. No. 12/869,573, filed Aug. 26, 2010 and entitled “SYSTEMS AND METHODS FOR INVARIANT PULSE LATENCY CODING”, U.S. patent application Ser. No. 12/869,583, filed Aug. 26, 2010, entitled “INVARIANT PULSE LATENCY CODING SYSTEMS AND METHODS”, U.S. patent application Ser. No. 13/117,048, filed May 26, 2011 and entitled “APPARATUS AND METHODS FOR POLYCHRONOUS ENCODING AND MULTIPLEXING IN NEURONAL PROSTHETIC DEVICES”, U.S. patent application Ser. No. 13/152,084, filed Jun. 2, 2011, entitled “APPARATUS AND METHODS FOR PULSE-CODE INVARIANT OBJECT RECOGNITION”, each incorporated herein by reference in its entirety, to produce post-synaptic detection signals transmitted over communication channels  1008 . In  FIG. 10 , the designators  1008 _ 1 ,  1008   —   n  denote output of the detectors  1002 _ 1 ,  1002   —   n , respectively. 
     In some implementations, the detection signals are delivered to a next layer of the detectors  1012  (comprising detectors  1012 _ 1 ,  1012   —   m ,  1012   —   k ) for recognition of complex object features and objects, similar to the exemplary implementation described in commonly owned and co-pending U.S. patent application Ser. No. 13/152,084, filed Jun. 2, 2011, entitled “APPARATUS AND METHODS FOR PULSE-CODE INVARIANT OBJECT RECOGNITION”, incorporated herein by reference in its entirety. In this implementation, individual subsequent layers of detectors may be configured to receive signals from the previous detector layer, and/or to detect more complex features and objects (as compared to the features detected by the preceding detector layer). For example, a bank of edge detectors may be followed by a bank of bar detectors, followed by a bank of corner detectors to enable alphabet recognition. 
     Individual ones of the detectors  1002  may output detection (e.g., post-synaptic) signals on communication channels  1008 _ 1 ,  1008   —   n  (with appropriate latency) that may propagate with different conduction delays to the detectors  1012 . The detector cascade of the implementation of  FIG. 10  may contain any practical number of detector nodes and detector banks determined, inter alia, by the software/hardware resources of the detection apparatus and complexity of the objects being detected. 
     The sensory processing apparatus implementation illustrated in  FIG. 10  may comprise lateral connections  1006 . In some implementations, the connections  1006  may comprise inhibitory connections configured in accordance with the activity-based plasticity rule described with respect to  FIGS. 4A-9 . 
     In some implementations, the apparatus  1000  may comprise feedback connections  1014 , configured to communicate context information from detectors within one hierarchy layer to previous layers, as illustrated by the feedback connections  1014 _ 1  in  FIG. 10 . In some implementations, the feedback connection  1014 _ 2  may be configured to provide feedback to the encoder  1024  thereby facilitating sensory input encoding, as described in detail in commonly owned and co-pending U.S. patent application Ser. No. 13/152,084, filed Jun. 2, 2011, entitled “APPARATUS AND METHODS FOR PULSE-CODE INVARIANT OBJECT RECOGNITION”, incorporated supra. 
     Some implementations of the computerized neuromorphic processing system, for operating a computerized spiking network (and implementing salient feature detection using the activity based plasticity methodology described supra), are illustrated in  FIG. 11A . The computerized system  1100  of  FIG. 11A  may comprise an input device  1110 , such as, for example, an image sensor and/or digital image interface. The input interface  1110  may be coupled to the processing block (e.g., a single or multi-processor block) via the input communication interface  1114 . In some implementations, the interface  1114  may comprise a wireless interface (cellular wireless, Wi-Fi, Bluetooth, RFID/NFC, and/or other wireless interface) that enables data transfer to the processor  1102  from remote I/O interface  1100 . One such implementation may comprise a central processing apparatus coupled to one or more remote camera devices comprising activity based plasticity and/or salient feature detection methodology of the disclosure. 
     The system  1100  further may comprise a random access memory (RAM)  1108  configured to store neuronal states and connection parameters and to facilitate synaptic updates. In some implementations, synaptic updates are performed according to the description provided in, for example, in U.S. patent application Ser. No. 13/239,255 filed Sep. 21, 2011, entitled “APPARATUS AND METHODS FOR SYNAPTIC UPDATE IN A PULSE-CODED NETWORK”, incorporated by reference herein by reference in its entirety. 
     In some implementations, the memory  1108  may be coupled to the processor  1102  via a direct connection (memory bus)  1116 , and/or via a high-speed processor bus  1112 ). In some implementations, the memory  1108  may be embodied within the processor block  1102 . 
     The system  1100  may further comprise a nonvolatile storage device  1106 , comprising, inter alia, computer readable instructions configured to implement various aspects of spiking neuronal network operation (e.g., sensory input encoding, connection plasticity, operation model of neurons, and/or other aspects). In one or more implementations, the nonvolatile storage  1106  may be used to store state information of the neurons and connections when, for example, saving/loading network state snapshot, or implementing context switching (e.g., saving current network configuration, which may comprise, inter alia, connection weights and update rules, neuronal states and learning rules, and/or other components) for later use and loading previously stored network configuration. 
     In some implementations, the computerized apparatus  1100  may be coupled to one or more external processing/storage/input devices via an I/O interface  1120 , such as a computer I/O bus (PCI-E), wired (e.g., Ethernet) and/or wireless (e.g., Wi-Fi) network connection. 
     It will be appreciated by those skilled in the arts that various processing devices may be used with computerized system  1100 , including but not limited to, a single core/multicore CPU, DSP, FPGA, GPU, ASIC, combinations thereof, and/or other processors. Various user input/output interfaces are similarly applicable to implementations of the invention including, for example, an LCD/LED monitor, touch-screen input and display device, speech input device, stylus, light pen, trackball, end the likes. 
       FIG. 11B , illustrates some implementations of neuromorphic computerized system configured for use with activity based plasticity and/or salient feature detection apparatus described supra. The neuromorphic processing system  1130  of  FIG. 11B  may comprise a plurality of processing blocks (micro-blocks)  1140 , where each micro core may comprise logic block  1132  and memory block  1134 , denoted by ‘L’ and ‘M’ rectangles, respectively, in  FIG. 11B . The logic block  1132  may be configured to implement various aspects of activity based plasticity and/or salient feature detection, such as the latency encoding described in U.S. patent application Ser. No. 12/869,573, entitled “SYSTEMS AND METHODS FOR INVARIANT PULSE LATENCY CODING”, filed Aug. 26, 2010, incorporated herein by reference in its entirety, neuron unit dynamic model, detector nodes  1022  if  FIG. 10A , and/or inhibitory nodes  1029  of  FIG. 10A . The logic block may implement connection updates (e.g., the connections  1014 ,  1026  in  FIG. 10A ) and/or other tasks relevant to network operation. In some implementations, the update rules may comprise rules spike time dependent plasticity (STDP) updates. The memory block  1024  may be configured to store, inter alia, neuronal state variables and connection parameters (e.g., weights, delays, I/O mapping) of connections  1138 . 
     One or more micro-blocks  1140  may be interconnected via connections  1138  and routers  1136 . In one or more implementations (not shown), the router  1136  may be embodied within the micro-block  1140 . As it is appreciated by those skilled in the arts, the connection layout in  FIG. 11B  is exemplary and many other connection implementations (e.g., one to all, all to all, etc.) are compatible with the disclosure. 
     The neuromorphic apparatus  1130  may be configured to receive input (e.g., visual input) via the interface  1142 . In one or more implementations, applicable for example to interfacing with a pixel array, the apparatus  1130  may be configured to provide feedback information via the interface  1142  to facilitate encoding of the input signal. 
     The neuromorphic apparatus  1130  may be configured to provide output (e.g., an indication of recognized object or a feature, or a motor command, e.g., to zoom/pan the image array) via the interface  1144 . 
     The apparatus  1130 , in one or more implementations, may interface to external fast response memory (e.g., RAM) via high bandwidth memory interface  1148 , thereby enabling storage of intermediate network operational parameters (e.g., spike timing, etc.). In one or more implementations, the apparatus  1130  may also interface to external slower memory (e.g., flash, or magnetic (hard drive)) via lower bandwidth memory interface  1146 , in order to facilitate program loading, operational mode changes, and retargeting, where network node and connection information for a current task may be saved for future use and flushed, and previously stored network configuration may be loaded in its place, as described for example in co-pending and co-owned U.S. patent application Ser. No. 13/487,576 entitled “DYNAMICALLY RECONFIGURABLE STOCHASTIC LEARNING APPARATUS AND METHODS”, filed Jun. 4, 2012, incorporated herein by reference in its entirety. 
       FIG. 11C  illustrates some implementations of cell-based hierarchical neuromorphic system architecture configured to implement activity based plasticity feature detection. The neuromorphic system  1150  of  FIG. 11C  may comprise a hierarchy of processing blocks (cells block)  1140 . In some implementations, the lowest level L1 cell  1152  of the apparatus  1150  may comprise logic and memory, and may be configured similar to the micro block  1140  of the apparatus shown in  FIG. 11B , supra. A number of cell blocks  1052  may be arranges in a cluster  1154  and communicate with one another via local interconnects  1162 ,  1164 . Individual ones of such clusters may form higher level cell, e.g., cell denoted L2 in  FIG. 11C . Similarly several L2 level clusters may communicate with one another via a second level interconnect  1166  and form a super-cluster L3, denoted as  1156  in  FIG. 11C . The super-clusters  1156  may communicate via a third level interconnect  1168  and may form a higher-level cluster, and so on. It will be appreciated by those skilled in the arts that hierarchical structure of the apparatus  1150 , comprising four cells-per-level, shown in  FIG. 11C  represents one exemplary implementation and other implementations may comprise more or fewer cells/level and/or fewer or more levels. 
     Different cell levels (e.g., L1, L2, L3) of the apparatus  1150  may be configured to perform functionality various levels of complexity. In some implementations, different L1 cells may process in parallel different portions of the visual input (e.g., encode different frame macro-blocks), with the L2, L3 cells performing progressively higher level functionality (e.g., edge detection, object detection). Different L2, L3, cells may perform different aspects of operating, for example, a robot, with one or more L2/L3 cells processing visual data from a camera, and other L2/L3 cells operating motor control block for implementing lens motion what tracking an object or performing lens stabilization functions. 
     The neuromorphic apparatus  1150  may receive visual input (e.g., the input  1002  in  FIG. 10 ) via the interface  1160 . In one or more implementations, applicable for example to interfacing with a latency encoder and/or an image array, the apparatus  1150  may provide feedback information via the interface  1160  to facilitate encoding of the input signal. 
     The neuromorphic apparatus  1150  may provide output (e.g., an indication of recognized object or a feature, or a motor command, e.g., to zoom/pan the image array) via the interface  1170 . In some implementations, the apparatus  1150  may perform all of the I/O functionality using single I/O block (e.g., the I/O  1160  of  FIG. 11C ). 
     The apparatus  1150 , in one or more implementations, may interface to external fast response memory (e.g., RAM) via high bandwidth memory interface (not shown), thereby enabling storage of intermediate network operational parameters (e.g., spike timing, etc.). The apparatus  1150  may also interface to a larger external memory (e.g., flash, or magnetic (hard drive)) via a lower bandwidth memory interface (not shown), in order to facilitate program loading, operational mode changes, and retargeting, where network node and connection information for a current task may be saved for future use and flushed, and previously stored network configuration may be loaded in its place, as described for example in co-pending and co-owned U.S. patent application Ser. No. 13/487,576, entitled “DYNAMICALLY RECONFIGURABLE STOCHASTIC LEARNING APPARATUS AND METHODS”, incorporated supra. 
     Exemplary Uses and Applications of Certain Aspects of the Disclosure 
     The activity based adaptive plasticity rule may advantageously aid unit selectivity during network operation during and/or subsequent to training. The efficacy of inhibitory connections between units responding to similar features may be increased and the efficacy of inhibitory connections between units responding to different features may be reduced. Inhibitory connection between units of the same selectivity (for example, red-red, green-green) may become stronger, while inhibitory connections between red-green units may become weaker. Strong inhibitory connections may cause red (green) units to sufficiently inhibit activity (spike output generation) of other red (green) units. At the same time, red/green units may not inhibit sufficiently the activity of green/red units, respectively. When the input comprises a large portion of features of one type (red features), the response of the red units may grow progressively weaker and/or less consistent, compared to the response of the green units. As a result, the saliency map may comprise greater emphasis at the green feature location. 
     The activity based saliency map may be provided to an image acquisition block. A saccade may be generated to the salient (for example, green) feature location. A saccade may be generated to an object/feature in the scene that is the most outstanding/oddball That is, to an object that is the least-like the others—for example: a woman in a group of men; an oddly dressed person in a group; a red flower in a group of yellow flowers; and or other. 
     An image acquisition block may be configured to process temporal sequences. The activity based saliency map may be used to identify “oddball” motions—for example, a person that moves against the crowd; a person that moves differently than the rest of the group; etc. 
     The activity based saliency map may be provided to other signal acquisition blocks, such as acoustic acquisition block. The orientation of the system may be directed to the most outstanding/distinct features—for example: female voice in a men&#39;s choir; a foreign language speaker in a group of native speakers. 
     It is appreciated by those skilled in the arts that above implementation are exemplary, and the framework of the disclosure is equally compatible and applicable to processing of other information, such as, for example information classification using a database, where the detection of a particular pattern can be identified as a discrete signal similar to a spike, and where coincident detection of other patterns influences detection of a particular one pattern based on a history of previous detections in a way similar to an operation of exemplary spiking neural network. 
     Advantageously, exemplary implementations of the present innovation are useful in a variety of devices including without limitation prosthetic devices, autonomous and robotic apparatus, and other electromechanical devices requiring sensory processing functionality. Examples of such robotic devises are manufacturing robots (e.g., automotive), military, medical (e.g. processing of microscopy, x-ray, ultrasonography, tomography). Examples of autonomous vehicles include rovers, unmanned air vehicles, underwater vehicles, smart appliances (e.g. ROOMBA®), etc. 
     Implementations of the principles of the disclosure are applicable to video data compression and processing in a wide variety of stationary and portable devices, such as, for example, smart phones, portable communication devices, notebook, netbook and tablet computers, surveillance camera systems, and practically any other computerized device configured to process vision data 
     Implementations of the principles of the disclosure are further applicable to a wide assortment of applications including computer human interaction (e.g., recognition of gestures, voice, posture, face, etc.), controlling processes (e.g., an industrial robot, autonomous and other vehicles), augmented reality applications, organization of information (e.g., for indexing databases of images and image sequences), access control (e.g., opening a door based on a gesture, opening an access way based on detection of an authorized person), detecting events (e.g., for visual surveillance or people or animal counting, tracking), data input, financial transactions (payment processing based on recognition of a person or a special payment symbol) and many others. 
     Advantageously, the disclosure can be used to simplify tasks related to motion estimation, such as where an image sequence is processed to produce an estimate of the object position (and hence velocity) either at each points in the image or in the 3D scene, or even of the camera that produces the images. Examples of such tasks are: ego motion, i.e., determining the three-dimensional rigid motion (rotation and translation) of the camera from an image sequence produced by the camera; following the movements of a set of interest points or objects (e.g., vehicles or humans) in the image sequence and with respect to the image plane. 
     In another approach, portions of the object recognition system are embodied in a remote server, comprising a computer readable apparatus storing computer executable instructions configured to perform pattern recognition in data streams for various applications, such as scientific, geophysical exploration, surveillance, navigation, data mining (e.g., content-based image retrieval). Myriad other applications exist that will be recognized by those of ordinary skill given the present disclosure. 
     It will be recognized that while certain aspects of the disclosure are described in terms of a specific sequence of steps of a method, these descriptions are only illustrative of the broader methods of the disclosure, and may be modified as required by the particular application. Certain steps may be rendered unnecessary or optional under certain circumstances. Additionally, certain steps or functionality may be added to the disclosed embodiments, or the order of performance of two or more steps permuted. All such variations are considered to be encompassed within the disclosure and claims herein. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art. The foregoing description is of the best mode presently contemplated. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the disclosure. The scope of the disclosure should be determined with reference to the claims.