bluuebunny/crossref_metadata_2025 huggingface dataset:
Separating Figure from Ground with a Parallel Network
Authors: Kienker Paul K , Sejnowski Terrence J , Hinton Geoffrey E , Schumacher Lee E
Published: January 2007

The differentiation of figure from ground plays an important role in the perceptual organization of visual stimuli. The rapidity with which we can discriminate the inside from the outside of a figure suggests that at least this step in the process may be performed in visual cortex by a large number of neurons in several different areas working together in parallel. We have attempted to simulate this collective computation by designing a network of simple processing units that receives two types of information: bottom-up input from the image containing the outlines of a figure, which may be incomplete, and a top-down attentional input that biases one part of the image to be the inside of the figure. No presegmentation of the image was assumed. Two methods for performing the computation were explored: gradient descent, which seeks locally optimal states, and simulated annealing, which attempts to find globally optimal states by introducing noise into the computation. For complete outlines, gradient descent was faster, but the range of input parameters leading to successful performance was very narrow. In contrast, simulated annealing was more robust: it worked over a wider range of attention parameters and a wider range of outlines, including incomplete ones. Our network model is too simplified to serve as a model of human performance, but it does demonstrate that one global property of outlines can be computed through local interactions in a parallel network. Some features of the model, such as the role of noise in escaping from nonglobal optima, may generalize to more realistic models.
An Anomalous Brightness Differentiation
Authors: Kanizsa Gaetano , Minguzzi Gian Franco
Published: January 2007

The two adjacent regions of a homogeneous surface divided by a thin line may appear different in brightness. The phenomenon is weak, but can be obtained and systematically studied under certain experimental conditions. Data suggest that the effect is influenced by both the spatial position and the relative size of the two regions. The phenomenon is worthy of further examination because it challenges current theories of brightness perception.
Eliminating the Haptic Oblique Effect: Influence of Scanning Incongruity and Prior Knowledge of the Standards
Authors: Appelle Stuart , Countryman Martin
Published: January 2007

Although the oblique effect has been conceptualized as a purely visual phenomenon, recent studies report its occurrence in a haptic matching task and present the hypothesis that differences in haptic orientational sensitivity might be responsible for the results. The possibility that procedural variables could be responsible was investigated. Specifically, the effect of prior knowledge of the stimulus orientation standards and of use of bilateral haptic exploration of standard and comparison orientations was examined. The results indicate that the reported oblique effect is reduced either when subjects are not informed which orientations will be tested, or when a unilateral matching procedure instead of a bilateral one is used. When both conditions are combined, the haptic oblique effect is eliminated. It is concluded that this particular manifestation of the oblique effect is not related to haptic sensitivity, but stems from (i) the use of well-established imagery as referent for a match (imagery for oblique stimulus orientations is inferior) and (ii) the inherently different scanning patterns required in bilateral exploration of obliques (percepts of standard and comparison obliques will be necessarily different).
An Assessment of Decision-Making as a Possible Factor in the Age-Related Loss of Contrast Sensitivity
Authors: Morrison James D , Reilly James
Published: January 2007

The possibility that changes in decision-making may contribute to the age-related decline in contrast sensitivity has been investigated in nineteen young subjects (ages 21–38 years) and twenty-seven old subjects (ages 55–92 years). A signal detection paradigm was employed in which the detection of stationary sinusoidal grating patterns was measured at 3 and 15 cycles deg−1 for a range of contrasts which were psychophysically equivalent for each subject. A decline in contrast sensitivity with age at the spatial frequencies studied was confirmed for contrast thresholds obtained both by the ascending method and from the 50% hit rate for detection of the grating pattern. The criterion adopted for decision-making, expressed as both β and percentage bias, did not change significantly between young and old subjects at 15 cycles deg−1. At 3 cycles deg−1, criterion β did not change significantly at x0.8, x1.0, or x1.2 contrast threshold, but at contrast giving 50% hit rate there was a significant increase with age. The percentage bias increased significantly at contrast threshold but not at 50% hit rate. It is inferred from the results that the loss of contrast sensitivity was not accountable in terms of the adoption of a more conservative criterion by older subjects. Hence visual loss in ageing is attributed to changes within the visual pathway rather than within higher decision-making centres.
Visual Reaction Time and High-Speed Ball Games
Authors: McLeod Peter
Published: January 2007

Laboratory measures of visual reaction time suggest that some aspects of high-speed ball games such as cricket are ‘impossible’ because there is insufficient time for the player to respond to unpredictable movements of the ball. Given the success with which some people perform these supposedly impossible acts, it has been assumed by some commentators that laboratory measures of reaction time are not applicable to skilled performers. An analysis of high-speed film of international cricketers batting on a specially prepared pitch which produced unpredictable movement of the ball is reported, and it is shown that, when batting, highly skilled professional cricketers show reaction times of around 200 ms, times similar to those found in traditional laboratory studies. Furthermore, professional cricketers take roughly as long as casual players to pick up ball flight information from film of bowlers. These two sets of results suggest that the dramatic contrast between the ability of skilled and unskilled sportsmen to act on the basis of visual information does not lie in differences in the speed of operation of the perceptual system. It lies in the organisation of the motor system that uses the output of the perceptual system.
Learning to See Stereokinetic Effects
Authors: Bressan Paola , Vallortigara Giorgio
Published: January 2007

The Saturn illusion is a stereokinetic effect that occurs when a flat pattern composed of a full ellipse with two symmetrical semirings is rotated slowly in the frontoparallel plane. Subjects report seeing an egg-shaped object inserted into a circular ring, and the two objects move solidly into 3-D space as a single rigid body. Inexperienced observers show a conspicuous delay before reaching this percept. Two experiments are reported in which it is shown that this incubation time progressively decreases with repeated exposures to the stimulus pattern. A certain amount of time (14 s on average) is, however, required to obtain the effect, even after six successive exposures. It is argued that this time, which is independent of the speed of rotation and is not further reducible, is a fixed entity and is needed to compute the most rigid 3-D solution from deformations in the 2-D image. The results are discussed in relation to current theories of perception of structure from motion.
Finding Parts within Figures: A Developmental Study
Authors: Kolinsky Régine , Morais José , Content Alain , Cary Luz
Published: January 2007

Preschool children, primary school children, and unschooled adults were tested on the part-probe task designed by Palmer. Relatively high scores were obtained with all groups on parts which had a ‘good’ relationship with the figure. However, the ability to find more deeply embedded segments was not present in the preschool children or in the unschooled adults. This indicates that the processes of postperceptual analysis necessary to find a part in a figure are neither built-in nor the consequence of mere cognitive growth, but depend on the instruction or experience usually provided in school. Such processes should not be confused with those that lead to form perception. Inspection of the part–figure pairs and of the corresponding detection scores suggests the importance of several stimulus properties.
Further Studies of the Café Wall and Hollow Squares Illusions
Authors: Woodhouse J Margaret , Taylor Steve
Published: January 2007

The effect of varying the contrast on the apparent convergence is measured for both the Café Wall and the Hollow Squares (Taylor—Woodhouse) illusions. The apparent convergence is dependent on the contrast, and also on the size of the stimulus, and varies in the same way for both illusions. This strengthens the argument that the illusions are not independent, as Taylor and Woodhouse originally claimed.

McCourt has discussed brightness induction as a basis of the Café Wall illusion. Consideration of this theory leads to some interesting examples of interactions of the two illusions, and to a further, very strong, variation of the illusion in a real-life situation.
The Vernier Aftereffect
Authors: Wolfe Jeremy M
Published: January 2007

Exposure to a vernier offset can cause a subsequently viewed straight contour to appear offset in the opposite direction. The size of this vernier aftereffect (VAE) varies systematically with the size of the adapting offset. The VAE may be a version of the tilt aftereffect.
Matching Forces: Constant Errors and Differential Thresholds
Authors: Jones Lynette A
Published: January 2007

A contralateral limb-matching procedure was used to study the perception of forces generated by the elbow flexor muscles. Subjects were required to generate forces ranging from 15 to 85% of their maximum voluntary contraction (MVC range: 169–482 N), and after achieving the target force to produce a force of the same perceived intensity with their contralateral arm. Under these conditions, subjects consistently overestimated the amplitude of the two lowest forces, and the most accurate matching of forces occurred in the middle of the response range (around 50% MVC). This pattern of constant errors could be explained in terms of an artifact of the starting position, which has been shown to influence the accuracy of judgements of stimulus magnitude. The Weber fraction for force calculated from the matching data was 0.07, which is within the range reported previously for weight. These thresholds are, however, considerably lower than those described for friction and the moment of inertia, the perception of which also involves the proprioceptive system.
Some Additional Predictions and Further Tests of the Marr—Ullman Model of Motion Perception
Authors: Webb Barbara , Wenderoth Peter
Published: January 2007

The Marr—Ullman model for motion detection in the human visual system functions by means of the dual input of polarity-specific edge detectors and luminance change detectors. Moulden and Begg (1986) found a polarity-specific motion aftereffect which they claimed provided support for this dual input model. The logic of their experiment is examined, and it is shown that several additional predictions arise from the Marr—Ullman model, which were not supported by Moulden and Begg's study. A more powerful experiment was carried out and these additional predictions were disconfirmed, although the polarity-specific effect did emerge. A consideration of alternative explanations of this effect led to a second experiment in which an attempt was made to discover the actual determinants of the effect. This revealed that polarity-specific units are unlikely to play any part in the phenomenon. It was concluded, in the light of this and other evidence, that one of a class of alternative models is more likely to be the actual mechanism for motion perception. However, careful consideration of the Marr—Ullman model indicated that it may be untestable in principle if various differentially weighted levels of neural integration are envisaged.
Illusory-Figure Lightness: Evidence for a Two-Component Theory
Authors: Parks Theodore E
Published: January 2007

Physical darkness gradients were introduced into an illusory-figure pattern which were sufficient to eliminate the illusory lightness effect otherwise seen there. Next, such a gradient was left in place along one edge of that figure while the other edges were returned to physical homogeneity with the surround. Rather surprisingly, the physical gradient still present along the unaltered edge was now overwhelmed by illusory lightness. It is argued that this anomaly suggests that illusory-figure lightness may be composed of two additive components, one of which is figure—ground contrast enhancement and the other of which is contingent upon that first component.
Three-Dimensional Anorthoscopic Perception
Authors: Fujita Naofumi
Published: January 2007

When a rotating 3-D wireframe object passes behind a narrow slit, it is often perceived as a 3-D object, even though only a small portion of it is visible at any one instant. This result constitutes a new finding in connection with both anorthoscopic perception and the perception of structure-from-motion.
Visual Illusory Productions with or without Amodal Completion
Authors: Bonaiuto Paolo , Giannini Anna Maria , Bonaiuto Marino
Published: January 2007

A new type of illusory contour is presented whose appearance is generated by the graphic representation of groups of human figures interacting in a coordinated manner with external reality. When numerous pictorial indicators of cause-effect relationships are provided, and appropriate techniques and sufficiently ambiguous observation conditions are used, hallucinatory objects congruent with expectations linked to the meaning of the configurations appear. There is thus a high-level semantic component that is active in the formation of visual illusory contours and is even capable of interacting with other known factors: brightness contrast, the number of elements, the degree of alignment of the elements, etc.

This new type of illusory contour fits current definitions and can be experimentally modified. The variations in subjective clarity scores are presented for a study in which twenty subjects observed nineteen experimental figures, certain variables of which were manipulated. The issue is worthy of further experimental investigation.
Comparison of Contrast Sensitivity Functions across Three Orientations: Implications for Theory and Testing
Authors: Long Gerald M , Tuck J Porter
Published: January 2007

The contrast sensitivity functions of a large group of observers ( N = 71) were determined for three orientations of test gratings: vertical, oblique, and horizontal. Comparison of group means indicated that, consistent with previous findings for the ‘oblique effect’, sensitivity was poorer for the oblique orientation—but only for the mid—high spatial frequencies. Correlation analyses indicated that contrast sensitivity for a particular spatial frequency at a given orientation was highly correlated with contrast sensitivity for that same frequency at the other two orientations. Factor analysis of the intercorrelations revealed two strong factors, a low frequency factor, and a mid-high frequency factor. Results are discussed in terms of: (a) the implications for contrast-sensitivity testing across orientations, (b) the basis for the oblique effect, and (c) a different type of evidence for a dichotomy among spatial-frequency channels that may reflect the distinction between X cells and Y cells or between the parvocellular and magnocellular systems.
The Spacing Illusion: A Spatial Aperture Problem?
Authors: Mather George , O'Halloran Alexandra , Anstis Stuart
Published: January 2007

A geometrical illusion in which the horizontal spacing between adjacent parallel lines in a row is underestimated when the lines are tilted away from vertical in a chevron configuration was investigated in two experiments. The perceived spacing was found to decrease as the tilt angle increased, consistent with the idea that separation judgements are influenced by the normal spacing between lines ie at right angles to the line orientation. It is proposed that this illusion reveals an analogue in spatial perception to the well-known aperture problem in motion perception. In establishing the separation of nearby or overlapping shapes in an image, the visual system cannot only rely upon the normal separation of contours belonging to each shape (as would be visible through small spatial apertures or receptive fields), since this varies with contour orientation. The system is therefore faced with a spatial aperture problem. The spacing illusion may arise because information usually available to solve the problem is absent in the illusion figure, or it may reflect a bias in favour of the orthogonal, which is adopted in the face of the ambiguity.
A Microgenetic Study of the Müller-Lyer Illusion
Authors: Schulz Thomas
Published: January 2007

In two experiments a decomposed Müller-Lyer pattern was used to measure the time course of the illusion. A partial report procedure was used to prevent the subjects from focusing only on parts of the pattern and to maximize visual processing. The Müller-Lyer figure was decomposed into two parts, its angles and its line. A configuration of three pairs of angles, each corresponding to a row in the usual partial report arrangement, was used. A line that did or did not fit the gap was shown with a variable delay (interstimulus interval, ISI). By this procedure the relevant row (line gap) was cued. The subject had to decide whether the line fitted or was too short/long. Two exposure times for the angles were used, 50 or 200 ms in one experiment and 50 or 500 ms in the other. The result of the first experiment, with outward-pointing fins, was a stable illusion for all values of ISI (25–400 ms) and all exposure times, with one significant exception: exposure for 50 ms with an ISI of 50 ms yielded an illusion peak. It was shown that this was not caused by a reduction in length-discrimination performance. In the second experiment, with inward-pointing fins, no such peak occurred. There was only a tendency for the illusion to vanish with zero ISI. The results are discussed with respect to ‘global to local’ theories of visual processing.
Auditory Localization in Teleoperator and Virtual Environment Systems: Ideas, Issues, and Problems
Authors: Durlach Nat
Published: January 2007

The increasing availability and use of advanced high-tech human-machine interfaces raise many interesting questions about what information should be presented to each sensory modality and how the information should be coded for a given modality. In this paper, attention is confined to the auditory component of the interface and, more specifically, to auditory localization. Both teleoperator systems and virtual-environment systems are considered, and attention is focused upon the opportunities and difficulties associated with the use of unnatural perceptual cues in these systems. Of central interest in this discussion is the use of such cues to improve resolution and thereby obtain systems with superlocalization capabilities.
Reorganization of Tactile Perception following the Simulated Amputation of One Finger
Authors: Benedetti Fabrizio
Published: January 2007

The tactile counterpart of diplopia has recently been described: tactile diplopia or diplesthesia. The human fingers show a rather precise organization of the cutaneous areas eliciting diplesthesia. In particular, these areas are very extensive between nonadjacent fingers (second and fourth, second and fifth, and third and fifth), suggesting that the illusory doubling depends on the lack of reciprocal interaction between cutaneous zones during manipulation. In the present study, four subjects agreed to explore and manipulate objects only through nonadjacent fingers for a period of up to six months. The amputation of the third finger was simulated by excluding it from active exploration by means of a bandage. After six months, the diplesthetic areas of the nonadjacent fingers decreased in size or completely disappeared. It is suggested that this reorganization of tactile perception is due to the increase in temporal correlation of the sensory inputs between nonadjacent fingers.
The Ceiling of the Church of St Ignatius and the Perception of Concave Surfaces
Authors: Massironi Manfredo , Savardi Ugo
Published: January 2007

This research describes two hitherto unobserved phenomena in the frescoes of the seventeenth century architect and painter, Andrea Pozzo, painted on the vaulted ceiling of the central nave of the Church of St Ignatius in Rome.

The present research also reports the results of two experimental studies on the problem of the perception of shapes projected on concave surfaces. A quantitative evaluation of the phenomena perceived from various points of observation is made by means of stimuli projected at various angles on a semicylindrical surface. The validity of the assumption of invariance, and in particular of the projective invariant called the cross-ratio, is discussed within the framework of ecological theories on perception.
Linear Vection in the Central Visual Field Facilitated by Kinetic Depth Cues
Authors: Telford Laura , Spratley Jonathan , Frost Barrie J
Published: January 2007

Illusory self-motion (vection) is thought to be determined by motion in the peripheral visual field, whereas stimulation of more central retinal areas results in object-motion perception. Recent data suggest that vection can be produced by stimulation of the central visual field provided it is configured as a more distant surface. In this study vection strength (tracking speed, onset latency, and the percentage of trials where vection was experienced) and the direction of self-motion produced by displays moving in the central visual field were investigated. Apparent depth, introduced by using kinetic occlusion information, influenced vection strength. Central displays perceived to be in the background elicited stronger vection than identical displays appearing in the foreground. Further, increasing the eccentricity of these displays from the central retina diminished vection strength. If the central and peripheral displays were moved in opposite directions, vection strength was unaffected, and the direction of vection was determined by motion of the central display on almost half of the trials when the centre was far. Near centres produced fewer centre-consistent responses. A complete understanding of linear vection requires that factors such as display size, retinal locus, and apparent depth plane are considered.
A Case of a Dual Frame of Reference
Authors: Navon David
Published: January 2007

It is demonstrated that observers may relate to two parts of the same object by using two different frames of reference. Subjects were asked to indicate directions within a model of a hallway in which signs were posted on a single prism. The majority of subjects interpreted a sign frontally facing them as indicating the direction which is ahead of them, yet they interpreted an adjacent sign that was slanted with respect to the frontal plane as indicating a direction which is at the same side of the line of sight as the sign is. This manifests a mixture of an egocentric and an object-centred frame of reference, that is reminiscent of the mixture of local spatial interpretations in impossible pictures. It is suggested that frames of reference are not necessarily unique in a given percept, and that they are not derived from a global computation.
Motion over the Retina and the Motion Aftereffect
Authors: Swanston Michael T , Wade Nicholas J
Published: January 2007

The motion aftereffect (MAE) was measured with retinally moving vertical gratings positioned above and below (flanking) a retinally stationary central grating (experiments 1 and 2). Motion over the retina was produced by leftward motion of the flanking gratings relative to the stationary eyes, and by rightward eye or head movements tracking the moving (but retinally stationary) central grating relative to the stationary (but retinally moving) surround gratings. In experiment 1 the motion occurred within a fixed boundary on the screen, and oppositely directed MAEs were produced in the central and flanking gratings with static fixation; but with eye or head tracking MAEs were reported only in the central grating. In experiment 2 motion over the retina was equated for the static and tracking conditions by moving blocks of grating without any dynamic occlusion and disclosure at the boundaries. Both conditions yielded equivalent leftward MAEs of the central grating in the same direction as the prior flanking motion, ie an MAE was consistently produced in the region that had remained retinally stationary. No MAE was recorded in the flanking gratings, even though they moved over the retina during adaptation. When just two gratings were presented, MAEs were produced in both, but in opposite directions (experiments 3 and 4). It is concluded that the MAE is a consequence of adapting signals for the relative motion between elements of a display.
The Poggendorff Illusion and Apparent Interparallel Extents
Authors: Day Ross H , Stecher Erica J , Parker Andrea L
Published: January 2007

An explanation of the Poggendorff misalignment effect in terms of apparent contraction of interparallel extent resulting from the Müller-Lyer illusion was tested in three experiments. Three of the eight stimulus figures had oblique transversals outside the parallels in the usual way, three had them inside, and two were controls consisting of the transversals only. Müller-Lyer forms were differently delineated between the parallels for the inside-transversal and outside-transversal figures, and were not delineated in the control figures. In the first experiment apparent misalignment occurred in four of the six parallel-line figures and in neither of the controls. In the second experiment oblique extent between the parallels was underestimated in six of the eight figures and right-angle extent was overestimated in all of them. The results of the third experiment showed that right-angle (horizontal) extent between the parallels without transversals is estimated without significant error. The data from the three experiments do not support the interparallel-extent explanation of apparent misalignment. Instead, the results are interpreted in terms of independent perceptual compromises, one involving alignment of the transversals and the other the distance between them.
Amodal Completion versus Induced Inhomogeneities in the Organization of Illusory Figures
Authors: Davi Marco , Pinna Baingio , Sambin Marco
Published: January 2007

An analysis is presented of a phenomenological model of illusory contours. The model is based on amodal completion as the primary factor giving rise to the illusory figure.

In the experiment, conducted by the method of paired comparisons, the same parameter was manipulated in two series of equivalent configurations. The first series yielded examples of amodal completion, the second examples of illusory figures. Three groups of subjects evaluated the magnitude of completion, the brightness contrast of the illusory figure, and the contour clarity of the illusory figure. A control experiment was conducted, which demonstrated that in these configurations amodal completion and amodal continuation behave in the same way.

Line displacement did not influence the brightness or the contour clarity of the illusory figures, though it influenced the magnitude of amodal completion. These results are in agreement with the energetic model developed by Sambin.
Four Questions of Time to Contact: A Critical Examination of Research on Interceptive Timing
Authors: Tresilian James R
Published: January 2007

Four questions concerning the use and perception of time to contact, tc, are identified. (i) Is tc information used in the timing of interceptive actions? (ii) If so, what control strategies are used? (iii) What are the perceptual sources of tc information and which of them do people use? (iv) How is the information extracted by the perceptual systems? Research relevant to these questions is reviewed and analysed. In connection with question (i), theoretical work on the special case of catching a moving object is analysed. It is concluded that treatments of catching which involve the use of tc information provide the best account of timing. In connection with question (ii), two types of control strategy suggested in the literature are identified: an intermittent strategy and a continuous strategy. Evidence for a continuous strategy is reconsidered and shown to be at least as well if not better accounted for by an intermittent strategy. Other empirical evidence for intermittent control is also discussed. In connection with question (iii) a simple unifying method is outlined with which all tc information so far presented in the literature can be derived, and examples are given. The viability of various types of information as sources of tc is examined by considering the errors which would result from their use. Finally, in connection with question (iv) the role of ‘looming detectors’ in the extraction of tc information is considered. These are frequently proposed as mechanisms for extracting the tc information provided by Lee's optic variable, tau. The analysis provided indicates that, despite the existence of a well-known and popular theory, due mainly to Lee, about how interceptive actions are timed, very little is actually known about perceptual timing. It is not yet certain whether tc information is used in interceptive timing tasks, what kinds of control strategies are involved, what sources of information people use to time their actions, or what perceptual processing is involved in the extraction of tc information.
Constraints on Haptic Integration of Spatially Shared Object Dimensions
Authors: Lederman Susan J , Klatzky Roberta L , Reed Catherine L
Published: January 2007

A study of the haptic integration of texture, shape, and hardness of nonplanar solid objects is reported. In experiment 1 the relative discriminability of the objects along each dimension was assessed. While levels of texture and shape were equally discriminable, hardness discriminations proved considerably more difficult. The extent of dimensional integration in a speeded classification task when both dimensions could be extracted from the same local patch was investigated in experiments 2 and 3. In experiment 2 subjects were initially encouraged to attend to a nontargeted dimension covarying with a targeted one. The nontargeted dimension was subsequently held constant (withdrawn). In experiment 3 dimensional variation was introduced which was uncorrelated with the targeted property during the course of categorization and hence discouraged subjects from attending to the nontargeted property. The results of these two studies converged in showing evidence of bidirectional dimensional integration between texture and shape and unidirectional integration when hardness was the targeted dimension. The failure to integrate hardness into categorization based on texture or shape was attributed to the difficulty of hardness discriminations. Integration effects in experiment 3 were not consistently smaller than those in experiment 2, which suggests a strong involuntary component to dimensional integration. The results of an analysis of the accompanying hand movements are interpreted in terms of constraints on dimensional integration. Implications for visual, cross-modal, and two-handed codimensional processing are also discussed.
Attentional Effects on Adaptation of Rotary Motion in the Plane
Authors: Shulman Gordon L
Published: January 2007

The effect of attention on the adaptation effects produced by stimuli rotating in the picture plane was examined in five experiments. In experiment 1, subjects performed a task either on a rotating adapting stimulus or on an irrelevant distractor stimulus. Adaptation of a subsequent ambiguous test stimulus was greater when the adapting stimulus was attended than when the irrelevant stimulus was attended. In experiments 2, 3, and 5, two adapting stimuli were presented, rotating in opposite directions, and subjects attended to one or the other. The direction of rotation of the ambiguous test stimulus depended on which adapting stimulus was attended. In experiment 4, the influence of eye movements in producing adaptation in ambiguous motion displays was determined by contrasting the effects of adaptation produced by dual adaptation stimuli rotating in the same or opposite direction. Adaptation effects were not predicted by eye movement hypotheses.
A Dissociation between Reaction Time to Sinusoidal Gratings and Temporal-Order Judgment
Authors: Tappe Thomas , Niepel Michael , Neumann Odmar
Published: January 2007

The effect of the spatial frequency (SF) of visual gratings on reaction time (RT) and temporal-order judgment (TOJ) was examined in three experiments. In experiment 1 the visual stimuli were vertical sinusoidal gratings with SFs between 2 and 8 cycles deg−1 and the comparison stimulus in the TOJ task was a 2300 Hz tone. Whereas SF had a highly significant effect on RT, it left TOJ completely unaffected. To test whether this dissociation was due to the sharp (high SF) horizontal edges of the gratings, a second experiment was carried out with circular stimuli with no sharp edges. These stimuli did produce an effect of SF on TOJ, but it was significantly smaller than was the effect on RT. In experiment 3 we confirmed that this difference was not due to differences in grating orientation between the first two experiments. These findings (a) solve discrepancies between findings reported in the literature and (b) strongly suggest that RT and TOJ cannot be regarded as converging operations for determining ‘visual latency’. This dissociation can best be accounted for by assuming that the output of early stimulus analysis can feed directly into the motor system (direct parameter specification), whereas the conscious representation that is used for TOJ is based on later integrative processes.
Guest Editorial: Perceptual Organisation and Object Recognition—POOR is the Acronym, Rich the Notion
Authors: Wagemans Johan , Kolinsky Régine
Published: January 2007

Instead of studying perceptual organisation and object recognition in relative isolation, they can be viewed as two highly related sets of processes performed by the visual system to achieve its goal of acquiring information about the world.

Fifteen papers devoted to specific subproblems within this active area of research have been brought together in two successive issues of Perception. Collectively they demonstrate that focusing on the functional interrelationships between perceptual organisation and object recognition will enrich our understanding of each of the subprocesses involved.

The editorial provides an overview of the papers together with a discussion on how they relate to one another. If a general message is to be extracted from this set of papers, it is that the reported findings and the speculations offered to explain them suggest that the visual system's processes cannot be characterised in general by simple dichotomies such as analytic versus wholistic, bottom-up versus top-down, local versus global, low-level versus high-level, parallel versus serial, etc. Instead, it appears that a wide variety of mechanisms is available to the visual system. Therefore, a complete understanding of its functioning will require careful examination of the circumstances within which one processing mechanism seems to be selected over another, depending on the available information, the task demands, and perhaps even the observer's individual characteristics.
The Relationship between Time of Arrival of Nontargets and Their Spatial Location: Evidence for Asymmetries in Visual Attentional Processing
Authors: Coyle Kieran
Published: January 2007

A brief advance of the presentation of distant nontargets has previously been shown to secure them an analysis, suggesting that even stimuli beyond the putative ‘spotlight’ of attention are analysed. In the present experiment nontargets were presented near to fixation or peripherally (at 0.6 or 1.9 deg of visual angle) for a duration of 17, 33, or 67 ms before being masked. After a subsequent period (SOA) of 0, 20, 40, 60, or 80 ms the target was presented at fixation. The results from the shortest nontarget duration show a time lag in the development of the effect of far nontargets on response to the target. At durations of 33 and 67 ms the identity of far nontargets has been established before masking takes place, since their effect is observable at zero SOA. However, while this effect remains relatively constant over SOAs of 20 to 80 ms it increases wth SOA in the near condition, suggesting that, although both near and far nontargets have been identified, it is only the near nontargets which are subject to further processing during the interval between nontarget and target presentations. The results favour a model of attention in which stimuli are passively selected and subject to additional processing on the basis of their spatial location rather than that the location or representation of distractor items are actively suppressed.
The Familiar-Size Cue to Depth under Reduced-Cue Viewing Conditions
Authors: Predebon John , Woolley Jacob Steven
Published: January 2007

The familiar-size cue to perceived depth was investigated in five experiments. The stimuli were stationary familiar objects viewed monocularly under otherwise completely darkened visual conditions. Perceived depth was measured directly with the method of verbal report and indirectly with the head-motion procedure. Although the familiar-size cue influenced verbal reports of the distances of the objects, it did not determine perceived depth as assessed with the head-motion procedure. These findings support the claim that familiar size is not a major determinant of perceived depth, and that cognitive or nonperceptual factors mediate the effects of familiar size on direct reports of depth and distance. Possible reasons for the failure of familiar size to influence the head-motion-derived measures of perceived depth are discussed with particular emphasis on the role of motion parallax in determining perceptions of depth and relative distance.
Mechanisms of Stereoscopic Processing: Stereoattention and Surface Perception in Depth Reconstruction
Authors: Tyler Christopher W , Kontsevich Leonid L
Published: January 2007

Consideration of the range of phenomena from studies of human stereopsis suggests that a five-stage model is required to provide a complete account of the processes involved, within which any stereoattention mechanism must operate. The information from the disparity field of the optical projections to the two eyes (stage 1) goes to a set of parallel Keplerian arrays of disparity detectors, each array selective for a different spatiotemporal property of the visual images (stage 2). Global interactions produce a cyclopean depth image that is cleaned of the spurious ghost images in the Keplerian arrays (stage 3) and that may then be processed for its (hypercyclopean) form elements (stage 4). Finally, there must be a stage of integration of the stereoscopic depth cues with monocular and kinesthetic depth cues to form the overall map of perceived distance (stage 5).

The fact that multiple cyclopean surfaces may be perceived as transparent implies that the stereoscopic system is not limited by a singular-surface constraint. However, it is unclear whether multiple surfaces can be seen simultaneously or whether only one surface is seen at a time by a selective-attention process, with the others perceived as a purely inchoate (qualitative) depth impression. New experiments on cueing of ambiguous stereocorrugations by singular flat planes suggest that selective stereoattention is a powerful mechanism. In fact, the results show that attention can be focused not just in horopteral planes but in a variety of depth configurations. Moreover, this attention focus may act as a tracking mechanism to allow perception of smooth cyclopean stereomotion, which has a frequency response up to ~ 5 Hz (in contrast to the ~15 Hz limit for detecting planar disparity shifts as jerky appearance and disappearance effects). Finally, the spatial limits of stereosurface reconstruction are explored with cyclopean targets to show some interesting asymmetries of the surface-wrapping process that may represent object-oriented constraints on depth reconstruction.
The Effects of Unilateral Visuospatial Neglect on Perception of Müller-Lyer Illusory Figures
Authors: Mattingley Jason B , Bradshaw John L , Bradshaw Judy A
Published: January 2007

Left visuospatial neglect after right hemisphere damage is a lateralised disorder of spatial perception and cognition. A study is reported of the extent to which patients with left visuospatial neglect are susceptible to the illusory effects normally elicited by Müller-Lyer figures, in which inducing fins are located on one end or on both ends of a horizontal line. Seven patients with left visuospatial neglect and seven normal controls were tested on a task of horizontal-line bisection in which stimuli consisted of plain lines of three lengths (100, 150, and 200 mm), randomly interleaved with lines with unilateral or bilateral fins. As a group, normals made accurate bisection judgments in the baseline (no-fins) condition, and exhibited significant illusory effects in both the unilateral-fin and the bilateral-fin conditions. In contrast, patients made substantial rightward errors in the baseline condition, consistent with their neglect of the left end of the line. However, as a group, patients still exhibited significant illusory effects with left-sided outward-projecting fins on 100 mm lines and with left-sided inward-projecting fins on 150 mm lines. Moreover, at least one patient exhibited consistent illusory effects both for inward-projecting and for outward-projecting left-sided fins at all line lengths. Normal illusory effects in patients were also obtained with stimuli containing unilateral right-sided and bilateral fins. The existence of such effects with inducing elements on the contralesional extremity of horizontal line stimuli suggests preservation of low-level, perhaps preattentive, perceptual mechanisms responsible for coding elementary visual features. The results may be relevant for an understanding of the influence of attentional factors on illusory perception.
The Discrimination of Dynamic Orientation Changes in Gratings
Authors: Wright Michael J , Gurney Kevin N
Published: January 2007

Thresholds were measured for discrimination of direction of a step angular rotation of gratings. The addition of simultaneous phase displacements (translation) had little effect on rotation thresholds for gratings over a considerable range; discrimination of rotation is unaffected by random directional translations an order of magnitude larger. Angular rotation discrimination thresholds increased with interstimulus interval (ISI). Thus discrimination is based at short ISIs (180 ms or less) on a percept of rotary motion, but at ISIs of several seconds by a spatial strategy (comparing static component orientations) relying on visual memory. Data points for the short-ISI region fell below the best-fitting straight line, and the slope of the short-ISI region of the curve was steeper than that of the long-ISI region. However, when either compound or simple gratings with uncorrelated spatial frequencies were used in the two stimulus frames, there was no evidence for a separate function at short ISIs. Orientation-change thresholds were measured for simple gratings as a function of contrast and spatial frequency. The contrast function showed saturation and the spatial frequency function was U-shaped. Rotation sensitivity for gratings is thus similar in its spatiotemporal properties to translation sensitivity. The findings support the proposal that rotation discrimination (at short ISIs) is achieved by a template mechanism combining signals from different directional detectors, rather than by cognitive comparison of the outputs of the directional mechanisms themselves.
Illusory Figures from Stereoscopically Three-Dimensional Inducers Depicting No Occlusion Event
Authors: Purghé Franco
Published: January 2007

It has been claimed that an illusory figure is prevented from occurring when there is contrary evidence to occlusion, eg when the inducers are pictorial representations of ‘complete’ three-dimensional (3-D) objects. However, it was recently shown that illusory figures may also be induced by such pictorially 3-D inducers. Here, further evidence on this point is presented. Two experiments were carried out. The first was aimed at showing that an illusory figure can be induced even by stereoscopically 3-D ‘complete’ inducers; the second was aimed at checking whether inducers that are stereoscopically seen as closer than the induced figure can contribute to strengthen the illusion. The results show that stereoscopically 3-D inducing patterns can affect the illusion both in the absence of any occlusion cue and when there is contrary evidence to occlusion. These conclusions seriously challenge all the interpretations that regard occlusion, or interposition, cues as necessary for the formation of illusory figures.
Capacity Limitations in Memory for Visual Locations
Authors: Lachter Joel , Hayhoe Mary
Published: January 2007

This paper examines people's ability to make judgments which require them to know the relative positions of objects that are not simultaneously visible is examined. It has previously been shown that people can accurately perform such a task. The current experiments test the capacity limits for such tasks. Two experiments were conducted that required subjects to make spatial judgments based on sequences of points presented two at a time. It was shown that, whereas subjects can perform accurately when memory for a small number of dots (about four) is required, increasing the number of dots results in a radical reduction in performance. This argues against both the idea that spatial memory is based on a linguistic description and the idea that it is based on an image-like representation. Rather it appears that one can form an accurate representation of the spatial properties of a small number of objects.
Foreshortening in Cube Drawings by Children and Adults
Authors: Nicholls Andrea L , Kennedy John M
Published: January 2007

The lengths of lines and the sizes of angles were measured in freehand drawings of cubes produced by 190 children and 158 adults. The lengths of oblique lines depicting receding cube edges were foreshortened relative to horizontal lines showing nonreceding edges. In the drawings from children aged 9 and 10 years the obliques were foreshortened by about 40%, compared with 30% in adults' drawings. The amount of foreshortening was not correlated with the angle at which the obliques were drawn. Line lengths were also foreshortened in ‘transparent’ drawings, which are often said to show ‘what is known’ about cube structure. One explanation of the results is that line lengths are foreshortened by children and adults to create the visual impression of equal-length cube edges, even in transparent drawings. This foreshortening fits with how the receding edges of a square face of a cube project to a vantage point. Children and adults who use foreshortening are not depicting the structure of cubes by matching features such as equal-length edges with similar features in the physical lines on the page, as has been suggested in some recent approaches to drawing development.