Perception

The effect of adaptation to pure relative motion was investigated for the motion aftereffect (MAE) of linear translation motion. In experiment 1, MAE induced by adaptation in the surrounding area was tested. The relative motion signal significantly increased the magnitude of MAE while local MAE in the surrounds was not affected. In experiment 2, MAE observed in the same adapted area was examined while local adaptation was cancelled out. Substantial MAE was found only when the test stimuli included the surroundings, which is considered to be favourable for relative motion mechanisms. These results clearly indicate that MAE is induced by adaptation to pure relative motion as well as by local motion. MAE should be regarded as a composite phenomenon reflecting multiple sites of adaptation including the local and the relative motion levels. The results also provide evidence for the existence of independent detecting mechanisms for relative motion processing.

An experiment was conducted to investigate the effects of perspective cue and binocular disparity on perceived angular and linear size. Following the ‘angular’ and ‘linear’ instructions, subjects matched the size of two squares, for which the binocular disparity between the centers of the squares and the configuration of the stimulus surrounding the squares were manipulated. Results showed that angular-size matches depended on the retinal-image size and the binocular disparity, and not on the visual-surround stimulus. Linear-size matches, on the other hand, depended on the visual-surround stimulus as well as on the image size and the binocular disparity. The visual-surround stimulus also affects the perceived depth between the test squares. These findings indicate that perceived angular and linear size depend on different processes that use different cues, and suggest that there is a causal relationship between perceived depth and perceived linear size.

In binocular vision horizontal magnification of one retinal image leads to a percept of three-dimensional slant around a vertical axis. It is demonstrated that the perception of slant is diminished when an occlusion interpretation is possible. A frontoparallel plane located in the immediate vicinity of a slanted surface in a location which allows a perception of occlusion reduces the magnitude of perceived slant significantly. When the same plane is placed on the other side, the slant perception is normal because there is no alternative occlusion interpretation. The results indicate that a common border between the occluder and a slanted surface is not a necessary condition for the reduction effect. If the edges are displaced and the edge of the slanted surface is placed in a location in which it could be occluded, the effect still appears.

In two experiments the luminance conditions for the occurrence of phenomenal transparency in achromatic flat patterns was studied. Let a, p, q and b be, respectively, the luminances of the parts A, P, Q, and B of a pattern comprising a transparent square on a two-part background, where P and Q are the parts of the square on backgrounds A and B, respectively. The results showed that |p – a|, |q – b|, and |p – q| were quantitative conditions of transparency. Metelli has proposed two ordinal conditions of transparency, |a – b| > |p – q| and p > q if a > b (or p < q if a < b). Alternatively, Masin and Fukuda have proposed the single ordinal condition p ∈ (a, q) [or q ∈ (p, b)]. The results showed that this second condition best predicted the occurrence of transparency.

Can visual similarity between shapes facilitate orientation priming? Five experiments are reported in which this possibility was explored by using novel two-dimensional shapes that formed homogeneous stimulus classes. After training on individual shapes in a canonical view, the recognition of these shapes was tested in several picture-plane orientations. In experiments 1 and 2 an identification task was used to replicate the classic finding obtained with the mirror-judgment task—that prior orientation cueing does not reduce the magnitude of orientation dependence in processing rotated shapes. The results of experiment 3, however, indicate that blocking trials by orientation is one condition in which orientation priming may be obtained. Experiment 4 builds on this result, and it is suggested that awareness of the blocking manipulation is not required to obtain orientation priming. In experiment 5 the mechanisms underlying this finding are explored, and evidence is offered that orientation priming is a consequence of representations that encode both shape and orientation. Such results may be considered as an extension to the ‘image-based’ approach to object recognition, demonstrating that generalization across exemplars may occur within recognition mechanisms that are viewpoint dependent.

The sex of a face is perhaps its most salient feature. A principal components analysis (PCA) was applied separately to the three-dimensional (3-D) structure and graylevel image (GLI) data from laser-scanned human heads. Individual components from both analyses captured information related to the sex of the face. Notably, single projection coefficients characterized complex differences between the 3-D structure of male and female heads and between male and female GLI maps. In a series of simulations, the quality of the information available in the 3-D head versus GLI data for predicting the sex of the face has been compared. The results indicated that the 3-D head data supported more accurate sex classification than the GLI data, across a range of PCA-compressed (dimensionality-reduced) representations of the heads. This kind of dual face representation can give insight into the nature of the information available to humans for categorizing and remembering faces.

The purpose of this study was to investigate the efficiency or speed of the frequently used L versus T visual search when sensory effects were controlled, ie ‘set size’ was not defined as the number of distractor patterns, but the number of distractors in the display was kept constant and the number of possible target positions varied. A search display consisted of an L-target among T-distractors, and the observer's task was to report the presence or absence of the target (experiment 1) or to identify it (whether the L-target was left-facing or right-facing; experiment 2). The observer was instructed prior to each stimulus block, about the display locations in which the target could appear. In both experiments, search time increased significantly with an increasing number of possible target locations, thus indicating that L versus T search is not ‘serial’ owing to sensory effects. Because, in the first two experiments, a search display was visible until the observer gave a response, ‘serial’ search might have resulted just from eye movements. Therefore, a control experiment was run in which display duration was limited to 150 ms. The results of this experiment showed that, even when eye movements were prevented, the search still occurred ‘serially’, ie response time increased as a function of the number of possible target positions.

Certain autistic children whose linguistic ability is virtually nonexistent can draw natural scenes from memory with astonishing accuracy. In particular their drawings display convincing perspective. In contrast, normal children of the same preschool age group and even untrained adults draw primitive schematics or symbols of objects which they can verbally identify. These are usually conceptual outlines devoid of detail. It is argued that the difference between autistic child artists and normal individuals is that autistic artists make no assumptions about what is to be seen in their environment. They have not formed mental representations of what is significant and consequently perceive all details as equally important. Equivalently, they do not impose visual or linguistic schema—a process necessary for rapid conceptualisation in a dynamic existence, especially when the information presented to the eye is incomplete.

Parks presented two example figures to illustrate that (i) familiarity can enhance illusory contour effects by completing an otherwise incomplete form and (ii) such contours are enhanced when their presence can explain an otherwise familiar but incomplete form. While familiarity probably does enhance illusory contours, additional perceptual factors may be involved in Parks's demonstrations.

In haptics, the perceived (phenomenal) flatness of a surface is strongly influenced by a previous surface which has been statically touched. The mechanisms underlying this haptic aftereffect of curved surfaces are investigated. It is shown that the representation of curvature abstracted from the sense of touch, ie a high-level representation, is not affected during the aftereffect. This is concluded because: (1) the aftereffect does not exhibit intermanual transfer; (2) the way in which two successive surfaces are touched can influence the magnitude of the aftereffect; and (3) it is not necessary to touch a surface—active muscular contraction can also result in a shift of the phenomenal flatness. Furthermore, it is suggested that the physiological process involved in the aftereffect is a central process, ie it is located in the brain but it is distinct for each hemisphere. This is supported by the findings that: (1) the decay rate of the aftereffect is not influenced by the degree of peripheral stimulation during the decay; and (2) the aftereffect does not transfer from the adapted hand to the unadapted hand.