bluuebunny/crossref_metadata_2025 huggingface dataset:
The Perceived Spatial Frequency, Contrast, and Orientation of Illusory Gratings
Authors: Georgeson Mark A
Published: January 2007

Illusory vertical gratings (V) and diagonal gratings (D) can be seen on a uniform field after inspection of a vertical grating. When using simultaneous and successive matching techniques the spatial frequencies of the V effect were found to be about 2 octaves below and 1–2 octaves above the adapting spatial frequency, but to be invariant with temporal frequency. At high adapting frequencies the D effect dominated, and was about 0·8 octave below the adapting spatial frequency, oriented about ±35° from vertical. The apparent contrast of V was about twice the value of the contrast threshold at its apparent spatial frequency. D effects seen during adaptation were about 60° from vertical and 3 octaves below the adapting frequency. The results are interpreted in terms of inhibition and disinhibition in an organized matrix of tuned channels, and the dominant pattern of inhibition in the matrix is inferred. Supporting evidence from neurophysiology, neuroanatomy, and psychophysics is briefly reviewed. An appendix deals with the question of interocular transfer of the aftereffect.
Perceptive Field Sizes and a New Version of the Hermann Grid
Authors: Berbaum Kevin , Chung Chan Sup
Published: January 2007

The Hermann grid has been explained in terms of concentric receptive fields and also used to determine the size of centers and surrounds in perceptive fields in humans. A new figure, which is simply the outlines of the squares of the Hermann grid, shows that receptive fields having a range of excitatory and inhibitory sizes may be responsible for the Hermann illusion.
Processing of Alphabetic Information Presented in the Fovea or the Periphery: Functional Visual Field and Cognitive Load
Authors: Williams Leonard J , Lefton Lester A
Published: January 2007

In a tachistoscopic reaction-time study that required subjects to respond ‘same’ or ‘different’ to vertically arrayed letter pairs, it was found that cognitive load (level of required match) and retinal eccentricity were both potent variables. It seems that subjects can process low-level information (physical matches) quite effectively out to at least 7 deg visual angle from fixation, in either direction. It was also demonstrated that higher-level processing may proceed fairly efficiently out to at least 4 deg from fixation. These estimates suggest that the abilities of the information processor to deal effectively with the periphery may have been underestimated in the past.
Simultaneous and Successive Contrast Effects in the Perception of Depth from Motion-Parallax and Stereoscopic Information
Authors: Graham Maureen , Rogers Brian
Published: January 2007

Prolonged inspection of a three-dimensional corrugated surface resulted in a successive contrast effect, or aftereffect, of depth, whereby a subsequently-viewed physically-flat test surface appeared to be corrugated in depth with the opposite phase to the adapting surface. The aftereffect occurred both when the depth was specified by motion parallax, in the absence of all other sources of depth information, and when it was specified solely by stereoscopic information. The depth aftereffect was measured by ‘nulling’ the apparent depth in the test surface with physical relative motion or binocular disparity until the test surface appeared flat. Up to 70% of the depth in the adapting surface was necessary to null the aftereffect.

Simultaneous contrast effects in the perception of three-dimensional surfaces were used to investigate the spatial interactions that exist in the processing of motion-parallax and stereoscopic information. A physically vertical surface appeared to slope in depth in the opposite direction to the slope of a surrounding surface. In this case up to 50% of the slope of the inducing surface was necessary to null the contrast effect. Similar results were again obtained for motion-parallax and stereoscopic depth.
Attentional Alterations of Slant-Specific Interference between Line Segments in Eccentric Vision
Authors: Jansen Robert D , Blum Gerald S , Loomis Jack M
Published: January 2007

Slant-specific interference between line segments in eccentric vision was altered by attentional methods in hypnotically susceptible observers. These methods included negative and positive posthypnotic hallucination of the inducing elements of the array, and nonhypnotic instruction to actively ignore the elements. Contributions to the experimental effects apparently derived in part from intrinsic inhibitory or facilitatory skill in the individual observer, sharpened by hypnotic training in hallucinations. Control observers with low and with high hypnotic susceptibility were not able to alter significantly the interference effect when attempting to simulate the hallucination conditions. The results seemingly link these attentional alterations to an early cortical stage of visual processing.
The Square-Wave Illusion and Phase Anisotropy of the Human Visual System
Authors: Leguire Lawrence E , Blake Randolph , Sloane Michael
Published: January 2007

A triangular-wave grating is perceived to fluctuate over time: at one moment it may appear veridical (ie triangular), at another it may more closely resemble a square-wave grating with rounded edges. In addition, the square-wave illusion itself is bistable, in that it sometimes appears to shift in phase by 180 deg. Experiments in which the phase and amplitude of the first three frequency components of the triangular-wave grating were independently varied showed that the square-wave illusion results from the relative phase of the frequency components. Adaptation to two frequency components in square-wave (sine) phase was found to reduce the illusion strength, and adaptation to triangular-wave (cosine) phase was found to increase the illusion strength. In addition, the square-wave adaptation effect spreads to nonadapted retinal areas. It is concluded that the square-wave illusion reflects a phase anisotropy in the human visual system that favors square-wave phase over other phase relations.
Locomotion of the Blind Controlled by Natural Sound Cues
Authors: Strelow Edward R , Brabyn John A
Published: January 2007

Measures of the accuracy of locomotion control were taken with blind and blindfolded sighted subjects using the natural auditory obstacle sense to locate a travel path. These measures were compared with the accuracy of visual guidance. While the blind show a greater skill than blindfolded sighted subjects in using auditory cues for guidance, auditory guidance is notably inferior to visual guidance and deteriorates markedly when smaller targets are used to define the travel path. The natural obstacle sense thus appears to give only a rudimentary perception of the presence of objects and does not provide sufficient spatial information to allow accurate locomotion control.
The Role of High Spatial Frequencies in Face Perception
Authors: Fiorentini Adriana , Maffei Lamberto , Sandini Giulio
Published: January 2007

The relevance of low and high spatial-frequency information for the recognition of photographs of faces has been investigated by testing recognition of faces that have been either low-pass (LP) or high-pass (HP) filtered in the spatial-frequency domain. The highest resolvable spatial frequency was set at 15 cycles per face width (cycles fw−1). Recognition was much less accurate for images that contained only the low spatial frequencies (up to 5 cycles fw−1) than for images that contained only spatial frequencies higher than 5 cycles fw−1. For faces HP filtered above 8 cycles fw−1, recognition was almost as accurate as for faces LP filtered below 8 cycles fw−1, although the energy content of the latter greatly exceeded that of the former. These findings show that information conveyed by the higher spatial frequencies is not redundant. Rather, it is sufficient by itself to ensure recognition.
Illusory Contours in Line Patterns with Apparent Depth Due to Either Perspective or Overlay
Authors: Day Ross H , Kasperczyk Richard T
Published: January 2007

An illusory contour along a partially delineated border in the form of an apparent ‘outside’ corner due to perspective was as strong as one along a similarly delineated border in the form of an edge due to overlay. An illusory contour along a border in the form of an apparent ‘inside’ corner, due probably to both perspective and overlay, was stronger than either. These outcomes suggest that apparent stratification from overlay is not necessary for the occurrence of illusory contours. They also accord with the view that apparent depth due to overlay or to perspective is equally effective in rendering partially delineated borders more prominent and, in consequence, the illusory contours that form along them stronger.
Discrimination of Spatiotemporal Patterns: The Role of Sustained and Transient Mechanisms
Authors: Shulman Gordon , Mulvanny Patrick
Published: January 2007

The role of sustained and transient mechanisms in pattern and flicker perception has been examined in two discrimination experiments. In the first, observers were required to analyze the temporal or spatial properties of a stimulus that highly stimulated either sustained or transient mechanisms. The results were only partially consistent with a model identifying sustained mechanisms with pattern perception and transient mechanisms with flicker perception. In the second experiment a subthreshold summation paradigm was used to explore interactions among those mechanisms that encode the temporal and spatial properties of a stimulus. The effect of a subthreshold temporal-frequency change on discrimination performance could not be explained by models in which temporal-frequency and spatial-frequency changes are evaluated separately and then combined.
Visual Apparent Movement: Transformations of Size and Orientation
Authors: Bundesen Claus , Larsen Axel , Farrell Joyce E
Published: January 2007

Sequential alternation between same-shaped stimuli differing in size (size ratio s) and orientation (angular difference v) produced a visual illusion of translation in depth and concurrent rotation. The minimum stimulus-onset asynchrony required for the appearance of a rigidly moving object was approximately a linearly increasing function of ( s− 1)/( s + 1) for simple translation in depth and a linearly increasing function of v for simple rotation. The extrapolated zero intercept was lower for translation than for rotation, but estimated transformation times were additive in combined transformations. The results suggest that (a) the processes of apparent translation in depth and apparent rotation are individually sequential-additive in structure, and (b) apparent translations and rotations are combined by fine-grained alternation of steps of apparent translation and steps of apparent rotation. Similar principles account for recent data on imagined spatial transformations of visual size and orientation.
Motion Parallax Information for Direction of Rotation in Depth: Order and Direction Components
Authors: Carpenter David L , Dugan Michael P
Published: January 2007

The work of Hershberger and his associates has demonstrated the effectiveness for judging direction of rotation in depth of several components of motion parallax. Confounding and conflicting results have made the status of two of these transformations, labeled Direction and Order, unclear. A study is reported in which the problems encountered in previous studies have been eliminated. College students correctly judged the direction of rotation of horizontal rows of dots which appeared to rotate in depth, which demonstrates that Direction and Order can, in fact, provide useful information about direction of motion in depth.
The Construction and Prediction of Psychophysical Power Functions for the Sweetness of Equiratio Sugar Mixtures
Authors: Frijters Jan E R , Ophuis Peter A M Oude
Published: January 2007

Psychophysical taste mixture models describe the relationship between the perceived intensities of the unmixed components and the intensity of the mixture. Three of these models are discussed. As all of these appear either to be internally inconsistent or lack sufficient generality, a simple alternative model has been developed especially for the prediction of the intensity of equiratio mixtures. This model was experimentally tested with glucose—fructose mixtures. On the basis of the data obtained it is shown that a psychophysical equiratio mixture function can be constructed in the same way as a power function for a single compound. The results show that the new mixture model can predict the functions for equiratio mixtures with great precision. Implications for mixture interaction phenomena are discussed.
Random-Walk and Accumulator Models of Psychophysical Discrimination: A Critical Evaluation
Authors: Heath Richard A
Published: January 2007

The accumulator model proposed by Vickers and the modified random-walk model proposed by Link and Heath are compared in their ability to account for confidence judgments in line-length discrimination tasks. The random-walk model proves to be a viable alternative to the accumulator model, and is able to account for the relationship between mean response time and confidence. The parameter estimation techniques available for the random-walk model are considered advantageous when compared with the accumulator model, because the predictions from the latter have been obtained with the use of computer simulation.
A New Reversible and Impossible Object
Authors: Katz Milton
Published: January 2007

A new reversible and impossible object that may be perceived as five distinct patterns is described.
Low-Level and High-Level Processes in the Perceptual Organization of Three-Dimensional Apparent Motion
Authors: Gerbino Walter
Published: January 2007

An experiment is described in which a bistable motion display is shown in four combinations of monoptic and dichoptic viewing. When two triangles are replaced by one of them, one of two competing phenomena can be seen: (i) local disappearance of the triangle that has not been replaced; (ii) a 3-D rotation of a rigid triangle from one location to another. The dependence of the first sensation on the duration of the interstimulus interval and on monocular availability of the local-identity information confirms previous evidence about the existence of two processes which mediate apparent motion. The localization of the high-level process, however, is questioned on the basis of a comparison of data obtained when motion information was monoptic or only dichoptic. As monoptic motion information seems more effective, the ‘figural’ higher process cannot be wholly located at the binocular level.
A New Random-Dot Stereo Illusion and its Application to the Anstis–Howard–Rogers Effect
Authors: Enright James Thomas
Published: January 2007

When the dynamic visual noise of an untuned television set is viewed with image defocusing (positive lenses) and with a narrow vertical obstruction partially blocking the pupil of one eye, the video ‘snow’ seems to separate into two stable surfaces at different depths, divided by a vertical discontinuity. The main features of this illusion can be quantitatively accounted for in terms of the optics of defocused images and the retinal disparities predicted from blur circles. A residual component of the illusion, however, which was perceived by a majority of subjects, cannot be readily explained by geometrical optics; it apparently reflects a more subtle aspect in the processing of visual images, corresponding to the Anstis–Howard–Rogers stereo-effect, in which local depth configurations can bias global stereopsis. Several novel aspects of that effect are described, based on use of this obstructed-pupil illusion as the evoking stimulus.
The Poggendorff Illusion in Descent from the Cross by Rubens
Authors: Topper David R
Published: January 2007

A comparison of the painting Descent from the Cross by Rubens with the earlier oil sketch reveals that Rubens discovered the Poggendorff illusion.
Flicker Haloes Observed with Subjective Borders
Authors: Remole Arnulf , Ng Albert S Y , Bathe Linda L , Padfield Paul D , Spafford Marlee M , Szymkiw Mary A
Published: January 2007

Subjective borders are known to behave quite similarly to real borders when the stimulus presents fragments of visually meaningful forms. There is less information on whether this also applies to unfamiliar stimulus elements. Thus, if a dark/bright stimulus border is presented intermittently at certain frequencies below flicker fusion, the bright border enhancement band increases greatly in width and takes on a textured appearance, resembling a halo streaming from the border. The percept is spontaneous and unlike anything experienced in real life.

Preliminary observations showed that the effect occurs also at subjective borders. The extent of the halo from the border was measured for various flicker frequencies and compared with similar measurements obtained with real borders. It was found that the extent varies with frequency in an identical manner for real and virtual borders. Also, the halo was judged equal in qualitative appearance for both kinds of border. The striking similarity between virtual and real effects in this respect is best explained in terms of physiological border perception processes, possibly instigated by a cognitive mechanism.
Stimulus Duration May Affect Partial Report Performance
Authors: Dixon Peter
Published: January 2007

Townsend, and Di Lollo and Moscovitch investigated the retention of item information in nearly identical variations of the partial report task. Whereas Townsend found a slight decrement in performance as the interval increased, Di Lollo and Moscovitch found a substantial increment. An experimental study of procedural differences that may have led to this discrepancy is reported. The results suggest that stimulus duration may have been responsible: Di Lollo and Moscovitch used extremely short durations (2 ms), while Townsend used longer durations (50 ms). This difference in durations may be important when the stimulus array and the partial report probe occur in close temporal contiguity.
Direction- and Velocity-Specific Responses from beyond the Classical Receptive Field in the Middle Temporal Visual Area (MT)
Authors: Allman John , Miezin Francis , McGuinness EveLynn
Published: January 2007

The true receptive field of more than 90% of neurons in the middle temporal visual area (MT) extends well beyond the classical receptive field (crf), as mapped with conventional bar or spot stimuli, and includes a surrounding region that is 50 to 100 times the area of the crf. These extensive surrounds are demonstrated by simultaneously stimulating the crf and the surround with moving stimuli. The surrounds commonly have directional and velocity-selective influences that are antagonistic to the response from the crf. The crfs of MT neurons are organized in a topographic representation of the visual field. Thus MT neurons are embedded in an orderly visuotopic array, but are capable of integrating local stimulus conditions within a global context. The extensive surrounds of MT neurons may be involved in figure–ground discrimination, preattentive vision, perceptual constancies, and depth perception through motion cues.
Poggendorff and Müller-Lyer Illusions: Common Effects
Authors: Greist-Bousquet Suzanne , Schiffman Harvey R
Published: January 2007

Previous investigations have shown that the magnitude of the Müller-Lyer illusion is a function of the linear and angular dimensions of the figure. If the Müller-Lyer and Poggendorff illusions share a common basis, then the magnitude of the Poggendorff illusion should similarly be a function of the analogous configural dimensions. A study is reported in which changes were made in the dimensions of the Poggendorff figure that are analogous to the dimensions of the Müller-Lyer figure: (i) the length of the parallel components (analogous to the wings of the Müller-Lyer figure); (ii) the length of the intertransversal extent (analogous to Müller-Lyer shaft length); and (iii) the angle formed between the parallel components and the intertransversal extent (analogous to the angle of wing attachment in the Müller-Lyer figure). The relationship between the magnitude of the illusion and the dimensions of the Poggendorff figure was found to be generally in line with previous findings relating to the Müller-Lyer illusion. Adaptation-level theory and the positive-context model accommodate the major findings of the present study.
Changes in the Coupling between Accommodation and Vergence Eye Movements Induced in Human Subjects by Altering the Effective Interocular Separation
Authors: Judge Stuart J , Miles Frederick A
Published: January 2007

It has usually been thought that the coupling between accommodation and convergence of the eyes is fixed and not modifiable by experience. Experiments are reported which show that the ratio of accommodative vergence to the accommodation stimulus, the stimulus AC/A ratio (one measure of the coupling), is elevated by brief periods (∼30 min) of experience of viewing the world through periscopic spectacles which increase the effective interocular separation. Experience of viewing through ‘cyclopean’ spectacles, which superimpose the line of sight of the two eyes, reduced the stimulus AC/A ratio in one subject and increased it in another, while it remained hardly affected in a third.
Dynamic Visual Capture: Apparent Auditory Motion Induced by a Moving Visual Target
Authors: Mateeff Stefan , Hohnsbein Joachim , Noack Thomas
Published: January 2007

Apparent motion of a sound source can be induced by a moving visual target. The direction of the perceived motion of the sound source is the same as that of the visual target, but the subjective velocity of the sound source is 25–50% of that of the visual target measured under the same conditions. Eye tracking of the light target tends to enhance the apparent motion of the sound, but is not a prerequisite for its occurrence. The findings are discussed in connection with the ‘visual capture’ or ‘ventriloquism’ effect.
The Optomotor Response and Induced Motion of the Self
Authors: Rock Irvin , Smith Deborah
Published: January 2007

Although the optomotor response in animals and induced motion of the self in humans occur under very similar stimulus conditions, they have not hitherto been related. Experiments with fish are reported which support the hypothesis that the optomotor response is based on the animal's attempt to nullify the unwanted experience of its own motion that is imposed upon it.
Encoding Speed of Visual Features and the Occurrence of Illusory Conjunctions
Authors: Broadbent Donald , Broadbent Margaret H P
Published: January 2007

Earlier studies have found that people show characteristic errors when asked to observe a rapid stream of events and to name the colour of a certain letter, or the letter in a certain colour. They tend to report the letter or colour from an event later in time than the correct one. This is not true, however, if they are asked to name the colour of a digit amongst letters, without knowing in advance the identity of the digit. There is also some evidence that the errors are symmetric if the location of the target is not known in advance. Three experiments are reported which show that this symmetry results from slow encoding of the colour as compared with the digit. It is still true that uncertainty about target identity does reduce the tendency to see the target in a later rather than an earlier colour. This effect is, however, superimposed on asymmetries resulting from coding speed, and the effect of uncertainty of location may be due only to this.
The Effects of Distinctiveness in Recognising and Classifying Faces
Authors: Valentine Tim , Bruce Vicki
Published: January 2007

In an earlier study it was found that distinctive familiar faces were recognised faster than typical familiar faces in a familiarity decision task. In the first experiment reported here this effect was replicated with the use of celebrities' faces rather than personally familiar faces. In the second and third experiments the effect of distinctiveness was found to reverse if the task was to distinguish between faces and jumbled faces. Subjects took longer to classify distinctive faces as faces than they did to classify typical faces. Thus distinctive faces were recognised faster, but were classified as faces more slowly than were typical faces, both when personally familiar faces and when famous faces were used as stimuli. These results are interpeted as evidence that faces are encoded by reference to a general face prototype.
Attention and Depth Perception
Authors: Kawabata Nobuo
Published: January 2007

The Necker cube is a line drawing with two possible solutions in depth perception. The process of interpreting a two-dimensional line drawing as a three-dimensional object was investigated using the Necker cube. Attention was directed to a local feature of a briefly presented cube, ie an angle at a vertex. The attended angle was perceived as a front part of the cube and other parts were interpreted so as to match this interpretation. Results show that the local feature to which attention was directed was interpreted first and then global features and other local features were interpreted so as to agree with the local feature interpreted initially. This suggests that the three-dimensional interpretation of the line drawing was made sequentially from the local feature to global structures.
The Pigeon's Discrimination of Movement Patterns (Lissajous Figures) and Contour-Dependent Rotational Invariance
Authors: Emmerton Jacky
Published: January 2007

The ability of pigeons to discriminate complex motion patterns was investigated with the aid of moving Lissajous figures. The pigeons successfully learned to differentiate two successively presented cyclic trajectories of a single moving dot. This suggests that they can recognize a movement Gestalt when information about shape is minimal. They also quickly learned a new discrimination between moving-outline stimuli with repetitively changing contour patterns. Contrasting results were obtained when the dot or outline stimuli were axis-rotated through 90°. Rotational invariance of pattern discrimination was clearly demonstrated only when moving contours were visible. Nevertheless, pigeons could discriminate the axis-orientation of a moving-dot or moving-outline pattern when trained to do so. Discrimination did not seem to depend on single parameters of motion but rather on the recognition of a temporally integrated movement Gestalt. The visual system of pigeons, as well as that of humans, may be well adapted to recognize the types of oscillatory movements that represent components of the motor behaviour shown by many living organisms.
Spatial Frequency and Selective Attention to Spatial Location
Authors: Shulman Gordon L , Wilson James
Published: January 2007

The effect of spatial attention on the detectability of gratings of different spatial frequency was measured using a probe technique. Three experiments are reported in which the detectability of full-field probe gratings was measured while subjects analyzed stimuli presented in either the central or the peripheral visual field. Selective attention to peripheral stimuli produced a facilitation at low frequencies and a decrement at high frequencies. These effects disappeared under forced-choice presentation.
Putting Order in the Impossible
Authors: Kulpa Zenon
Published: January 2007

The class of visual illusions called ‘impossible figures’ (illusory spatial interpretations of pictures) is analyzed in order to introduce an ordering into the great variety of such figures. Such an ordering facilitates reference, unifies terminology, and establishes a conceptual framework for further investigations of the subject, making easier the choice and systematic generation of various types of figures (for example, in systematic psychological experiments). First, the notion of ‘impossible figure’ is defined and certain other related classes of figures (so-called ‘likely’ and ‘unlikely’ figures) are distinguished. Second, the fundamental ‘impossibility sources’ are identified as elementary ‘building blocks’ of all impossible figures. Finally, two broad classes of impossible figures, multibars (or ‘impossible polygons’) and striped figures, are briefly described.
Perception of Positional Relationships between Line Segments in Eccentric Vision
Authors: Saarinen Jukka
Published: January 2007

The encoding of positional relationships between pattern elements in eccentric vision was studied with different patterns consisting of the same short line segments in different positions. In each trial two stimulus patterns were flashed one above the other and the subject had to decide whether the patterns were identical or mirror symmetric (experiment 1) or whether the patterns were the same or different (experiments 2 and 3). The ability to discriminate between identical and mirror symmetric patterns was reduced in eccentric vision, even when the patterns were size-scaled according to the cortical magnification factor and thus the patterns were similarly visible at the different eccentricities. The results agree with the notion that eccentric vision is inferior to central vision in tasks which require proper encoding of information about the relative positions of pattern elements.
The Apparent Size of Three-Dimensional Objects and Their Silhouettes: A Solid-Superiority Effect
Authors: Walker James T , Walker M Jill
Published: January 2007

A solid object looks larger than its outline or silhouette under many viewing conditions. This solid-superiority effect may result from the assimilation or confusion of visual contours within the projection of a three-dimensional object on the picture plane. An aspect of the Müller-Lyer illusion may also play a role.
The Perception of an Optical Flow Projected on the Ground Surface
Authors: Flückiger Michelangelo , Baumberger Bernard
Published: January 2007

In most experiments in which the importance of visual control on postural stability is studied, optical stimuli attached to vertical surfaces are used. Analyses of long-term standing readjustments generally involve back-and-forth movements of a visual scene or its projection on vertical circular screens. In a natural environment, however, visual information is largely available from the ground. The aim of the experiment reported was to assess the effect of a flow pattern simulating an open outdoor setting on motion perception and postural control. Subjects were presented with an optical texture projected onto the ground. Periods of motionless texture alternated with equivalent durations of unidirectional flows. The change of position of the subject's centre of gravity over time was recorded on a force platform. Results show that the direction of body sway corresponded with that of texture motion. Important aftereffects, as shown in linear vection experiments, were also observed. However, the latency of postural responses was much shorter than with prolonged unidirectional flows produced in other locations of the visual environment. The hypothesis of an ecological specificity of the flows perceived on the ground during terrestrial displacements is discussed.
Characteristic Views and the Visual Inspection of Simple Faceted and Smooth Objects: ‘Tetrahedra and Potatoes’
Authors: Perrett David I , Harries Mark H
Published: January 2007

The way in which human subjects distribute their time when attempting to learn the surface appearance of objects placed on a stand free to rotate about its vertical axis was investigated. Experiments were undertaken to establish whether observers concentrate their time on particular views and, if so, to determine the image characteristics of the preferred views. For tetrahedra, subjects concentrated on views which presented a face or an edge centred on the line of sight. Both of these views were symmetric about the vertical axis. For potatoes as examples of opaque smooth objects, subjects concentrated on four views in which the object's principal (long) axis was oriented side-on or end-on to their line of sight. For such views the horizontal width (and surface area) of the object's image had maximum and minimum values. Preferred views were not systematically related to views defined as stable from the appearance of surface boundaries or ‘singularities’.
Circular Vection is Independent of Stimulus Eccentricity
Authors: Post Robert B
Published: January 2007

The sensation of self-rotation induced by viewing a surround rotating about the observer's vertical axis (circular vection or CV) was investigated with equal-area stimuli located in either the central, the mid-peripheral, or the far-peripheral visual field. Magnitude estimation responses indicated greater CV with larger stimulus area, but no significant differences in CV sensations as a function of stimulus eccentricity. This pattern of results does not support the belief that CV is dominated by peripheral stimulation when equal-area stimuli are compared.
Planarity and Segmentation in Stereoscopic Matching
Authors: Mitchison Graeme
Published: January 2007

The matching of stereograms which contain periodic patterns suggests ways in which the stereo correspondence problem may be solved in human vision. The stereograms seem to be segmented by coarse-scale features. Within each segment a set of matches approximating a plane is chosen. In regions with periodic patterns there may be many such planar sets, and the disparity of coarse-scale features seems to guide the choice of a particular set. This emphasis on planarity may reflect the occurrence of correlation-like operations in cortical neurons. An attractive possibility is that segmentation effectively delimits areas of the visual field within which disparities are likely to be slow changing (eg local tangent planes to surfaces) so that the correlation sums evaluated in a segment can give the best estimate of depth. A mechanism of this kind cannot account for all of stereo matching, since not all visual objects are well described by ensembles of planes. But it is likely to be a component of the matching system which is particularly important where images are ‘noisy’ and averaging is needed to extract reliable disparities.
Adaptation to Telestereoscopic Viewing Measured by One-Handed Ball-Catching Performance
Authors: Judge Stuart J , Bradford C Mary
Published: January 2007

A one-handed ball-catching task was used to study the disturbance of depth judgement induced by telestereoscopic viewing (ie viewing with increased effective interocular separation), the recovery of performance with experience in the telestereoscope, and the errors that subsequently arose when the telestereoscope was removed. The ball's trajectory was variable so that subjects had to control both the position and the timing of the grasp in order to catch the ball. On first wearing the telestereoscope, subjects closed the hand when the ball was approximately twice as far away from the eyes as the hand was. After fewer than twenty trials in the telestereoscope subjects were closing the hand at approximately the correct time and place, although rather more trials were needed for ball-catching performance to recover to normal. When the telestereoscope was removed there was an aftereffect, with subjects making the opposite errors to when they began the task. The existence of an aftereffect shows that the process of adaptation involves reevaluation rather than neglect of the misleading binocular information. Helmholtz's theory that telestereoscopes cause the world to be perceived as a scale model is considered. Initial misreaching is roughly consistent with this theory, but there are insufficient data to test it rigorously. Data from the aftereffect phase are clearly inconsistent with the theory. The results confirm the importance of binocular information in dynamic motor tasks, such as ball catching.
Depth Interpolation with Sparse Disparity Cues
Authors: Würger Sofia M , Landy Michael S
Published: January 2007

The interpolation of stereoscopic depth given only sparse disparity information was investigated. The basic stimulus was a rectangle with zero disparity at one edge, and 20 or 30 min visual angle disparity at the other. The depth assigned to the ambiguous intervening locations was measured by means of a small briefly-flashed binocular comparison spot. For a stimulus consisting of a uniform rectangle presented on a background of random dots with zero disparity, interpolated depth was greater for a high mean contrast between rectangle and background than for a low mean contrast. Relative to a linear interpolation between the edges, a larger difference in edge disparity resulted in poorer depth interpolation. Depth interpolation based on rivalrous information was examined by filling the stimulus rectangle with narrow-band filtered noise which was uncorrelated between the two eyes. Four different passbands which were matched in apparent contrast were investigated. The results demonstrate that the rivalrous low-spatial-frequency content was resistant to interpolation; rivalrous high spatial frequencies did not interfere with depth interpolation. High-spatial-frequency stimuli yielded a percept similar to the uniform-field condition, whereas low-spatial-frequency stimuli lay in a depth plane near or even behind the background. In the latter case a transparent plane was perceived which was linearly interpolated between the two edges, and which floated above the rivalrous noise.
Olfactory Adaptation and Recovery in Old Age
Authors: Stevens Joseph C , Cain William S , Schiet Franc T , Oatley Michael W
Published: January 2007

Four experiments are reported in which it is shown that elderly adults are more prone than young adults to olfactory adaptation and are slower to recover threshold sensitivity. The first three experiments differed in detail, but had in common an initial threshold determination for 1-butanol, a 30 s exposure to a concentration twenty-seven times threshold, followed by repeated presentation of the initial threshold level at various intervals after adaptation. In three experiments accuracy of forced-choice discrimination was poor immediately after adaptation but tended to improve with time, and considerably faster in the young than in the elderly. In the fourth experiment, groups of twenty-three elderly and twenty-five young subjects threshold-matched for pyridine were compared. The subjects participated in three sessions in which pyridine was infused into a test chamber at either 2.5, 1.25, or 0 L min−1 (sham session). At 2.5 L min−1 both groups were able to track the buildup of odor intensity during infusion and its decline after infusion. In contrast, at 1.25 L min−1 only the young were able to track odor intensity, even though the concentration rose above initial threshold levels.
Orientation Illusions Induced by Briefly Flashed Plaids
Authors: Wenderoth Peter , van der Zwan Rick , Johnstone Syren
Published: January 2007

Orientation illusions which occur when a vertical grating is surrounded by a plaid can be induced either by one of the plaid's orthogonal component gratings or by a virtual axis of symmetry of the plaid, whichever is nearest vertical. In six experiments in which such illusion displays were flashed for durations between 15 and 405 ms, it was found that when these two-dimensional illusions are induced by a component grating (direct effects) the illusions increase monotonically as duration decreases, from 1°–2° to about 6°–7°, over this range. Effects induced by axes of symmetry (indirect effects), in contrast, begin to occur only at longer durations: for short exposures, illusions are directionally opposite and large, similar to direct effects. These results suggest that only plaid-component-selective mechanisms operate at the shortest exposure durations and that additional time is required to extract more global higher-order pattern structure. The data are discussed in relation to sustained and transient mechanisms and also with respect to recent reports of more global processing mechanisms in extrastriate cortex and related data on one-dimensional tilt illusions.
Illusory Contours from Pictorially Three-Dimensional Inducing Elements
Authors: Parks Theodore E , Rock Irvin
Published: January 2007

Illusory-figure patterns which are composed of pictorial elements representing three-dimensional partial disks are sometimes effective and sometimes not. When they are not effective, it is apparently because they contain information that contradicts the presence of an occluding figure and/or because all of the edges within the pattern are seen as edges of various pictured surfaces of the elements.
Sensitivity to the Displacement of Facial Features in Negative and Inverted Images
Authors: Kemp Richard , McManus Chris , Pigott Tara
Published: January 2007

Subjects have previously been reported to show difficulties in recognising faces which are either inverted or in photographic negative. Experiments are reported in which a two-alternative forced-choice technique was used to measure sensitivity for distinguishing faces which have been modified by having the eyes moved vertically or horizontally. Subjects were less sensitive to such changes for inverted faces or negative faces, and were even less sensitive for faces that were both inverted and negative. No such effects were found for a control stimulus consisting simply of three solid circles in the same positions as the eyes and mouth of a face. When the stimuli consisted of eyes, nose, and mouth, but without a surround, no evidence of inversion or negation effects was found, which suggests that a facial surround is necessary. When the stimulus consisted of a facial surround with the eyes, nose, and mouth replaced by solid circles, effects of negation were found, but no effects of inversion. This dissociation of the effects of negation and inversion may suggest that they are the result of different underlying mechanisms.
Retinal Mechanisms in the Perception of Subjective Contours: The Contribution of Lateral Inhibition
Authors: Coren Stanley
Published: January 2007

One mechanism frequently proposed for the creation of subjective contours and their related brightness effects involves lateral neural interactions on the retina, such as the lateral inhibitory effects that underlie brightness contrast. Subjective contour stimuli were displayed under an intermittent light source, with rapid onset and slow offset as has been shown to increase lateral inhibitory interactions by allowing summation of neural onset transients. A sample of forty subjects, using magnitude estimates, reported increased subjective contour clarity and brightness effects under these exposure conditions. The effects were larger for relative brightness differences than for contour visibility. It appears that this technique may have applications in exploring retinal contributions to other aspects of the perception of subjective contours.
A Dynamic Model for Anomalous Figures: The Shape of Line-Induced Brightness Modifications
Authors: Pinna Baingio , Sambin Marco
Published: January 2007

It is recognized that a fundamental role in the perception of anomalous figures is played by the intensity and shape of brightness modifications induced by line ends. The aim of this work was to study the structure of these modifications experimentally, by using variously arranged dots as probes. It was thus assumed that dots can measure activations generated inside abrupt line ends. The results show distribution of activation which differs according to dot distance and angle with respect to the continuation of the line near its end. These data do not agree with the predictions of information processing models in the literature on anomalous figures, which are based on perceptually postulated figures accounting for unlikely gaps. However, they do agree with the dynamic model proposed here, which is based on the idea that certain figure characteristics, eg the differential brightness of anomalous figures, depend on activation distribution which in turn depends on the organization of the forces in play. This idea is rooted in Gestalt theory. Another model supported by our experimental data is Grossberg's neural dynamic approach. In this case too, the basic idea is that of activation distribution which depends on the interaction of complex neural networks functioning according to special algorithms.
Induced Motion: Isolation and Dissociation of Egocentric and Vection-Entrained Components
Authors: Heckmann Thomas , Howard Ian P
Published: January 2007

Induced motion (IM) is illusory motion of a stationary test target opposite to the direction of the real motion of the inducing stimulus. We define egocentric IM as an apparent motion of the test target relative to the observer, and vection-entrained IM as an apparent motion of a stationary object along with an apparent motion of the self (vection) induced by the same stimulus. These two forms of IM are often confounded, and tests for distinguishing between them have not been devised. We have devised such tests. Our test for egocentric IM relies on evidence that this form of IM is due mainly to a misregistration of eye movements when optokinetic nystagmus (OKN) is inhibited, and on evidence that OKN is evoked only by stimuli in the plane of convergence. Our test for vection-entrained IM relies on evidence that vection is evoked only by the more distant of two superimposed inducing stimuli. Thus we found egocentric IM to be induced without vection or vection-entrained IM when subjects converged on a foreground moving display with a stationary display in the background, and vection-entrained IM to be induced without egocentric IM when subjects converged on a stationary-foreground display with a moving display in the background. The two types of IM were evoked in opposite directions at the same time when subjects converged on a foreground moving display while a background display moved in the opposite direction. The two forms of IM showed no signs of interaction, and we conclude that they rely on independent motion mechanisms that operate within distinct frames of reference. A control experiment suggested that the depth adjacency effect in IM is determined by the depth adjacency of the inducing stimulus to convergence, not just to the test target.
Evidence for Complete Translational and Reflectional Invariance in Visual Object Priming
Authors: Biederman Irving , Cooper Eric E
Published: January 2007

The magnitude of priming on naming reaction times and on the error rates, resulting from the perception of a briefly presented picture of an object approximately 7 min before the primed object, was found to be independent of whether the primed object was originally viewed in the same hemifield, left—right or upper—lower, or in the same left—right orientation. Performance for same-name, different-examplar images was worse than for identical images, indicating that not only was there priming from block one to block two, but that some of the priming was visual, rather than purely verbal or conceptual. These results provide evidence for complete translational and reflectional invariance in the representation of objects for purposes of visual recognition. Explicit recognition memory for position and orientation was above chance, suggesting that the representation of objects for recognition is independent of the representations of the location and left—right orientation of objects in space.