Perception

Illusory bands at a luminance transition in space (ie an edge) are well known. Here we demonstrate illusory bands of enhanced orientations or spatial frequencies at transitions between higher-contrast and lower-contrast image content along the orientation and spatial-frequency dimensions—the dimensions of cortical spatial coding. We conclude that this illusion is a consequence of cortical-level suppression of units of similar orientations and spatial frequencies and serves to aid texture segmentation while providing efficient neural coding.

In the occlusion illusion, the visible portion of a partly occluded object (eg a semicircle partly hidden behind a rectangle) appears to be significantly larger than a physically identical region that is fully visible. This illusion may occur either because the visual system ‘fills in’ a thin strip along the occluded border (the partial-modal-completion hypothesis) or because the partly occluded object is perceived as farther away (the apparent-distance hypothesis). We measured the magnitude of the occlusion illusion psychophysically in several experiments to investigate its causes. The results of experiments 1–3 are consistent with the general proposal that the magnitude of the illusion varies with the strength of the evidence for occlusion, supporting the inference that it is due to occlusion. Experiment 4 provides a critical test between apparent-distance and partial-modal-completion explanations by determining whether the increase in apparent size of the occluded region results from a change in its perceived shape (due to the modal extension of the occluded shape along the occluding edge, as predicted by the partial-modal-completion hypothesis) or from a change in its perceived overall size (as predicted by the apparent-distance hypothesis). The results more strongly support the partial-modal-completion hypothesis.

In the Delboeuf illusion, a circle judged initially has a weaker effect of size induction than a circle judged subsequently (the judgment-order effect). This effect has been attributed to differential allocation of visual attention (Hamada et al, 2002 Japanese Journal of Psychology 73 58–63, in Japanese). To establish the influence of attention, in experiment 1 we examined whether the effect occurred mandatorily once the outer circle was attended to, or whether it was necessary to direct attention specifically to the size of the area of the outer circle. Observers trisected the circumference of the outer circle thus attending to the outer circle in terms of its circumference, but ignoring its area. The illusion was stronger when the inner-circle area estimation was followed by the outer-circle area estimation than when the inner-circle area estimation was followed by the trisection task. In experiment 2 this result was replicated by using diameter judgment, instead of the size of the area. These findings indicate that mere allocation of attention to the outer circle contour is not sufficient to produce the judgment-order effect. Rather, attention must be specific to the task-relevant dimension, in this instance the visual area, to be effective.

Many objects in natural scenes have textures on their surfaces. Contrast of the texture surfaces (the texture contrast) reduces when the viewing distance increases. Similarly, contrast between the surfaces of the objects and the background (the area contrast) reduces when the viewing distance increases. The texture contrast and the area contrast were defined by the contrast between random dots, and by the contrast between the average luminance of the dot pattern and the luminance of the background, respectively. To examine how these two types of contrast influence depth perception, we ran two experiments. In both experiments two areas of random-dot patterns were presented against a uniform background, and participants rated relative depth between the two areas. We found that the rated depth of the patterned areas increased with increases in texture contrast. Furthermore, the effect of the texture contrast on depth judgment increased when the area contrast became low.

Vertical binocular disparity provides a useful source of information allowing three-dimensional (3-D) shape to be recovered from horizontal binocular disparity. In order to influence metric shape judgments, a large field of view is required, suggesting that vertical disparity may play a limited role in the perception of objects projecting small retinal images. This limitation could be overcome if vertical disparity information could be pooled over wide areas of 3-D space. This was investigated by assessing the effect of vertical disparity scaling of a large surround surface on the perceived size and 3-D shape of a small, central object. Observers adjusted the size and shape of a virtual, binocularly defined ellipsoid to match those of a real, hand-held tennis ball. The virtual ball was presented at three distances (200, 325, and 450 mm). Vertical disparities in a large surround surface were manipulated to be consistent with a distance of 160 mm or infinity. Both shape and size settings were influenced by this manipulation. This effect did not depend on presenting the surround and target objects at the same distance. These results suggest that the influence of vertical disparity on the perceived distance to a surface also affects the estimated distance of other visible surfaces. Vertical disparities are therefore important in the perception of metric depth, even for objects that in themselves subtend only small retinal images.

The sequential-surface-integration-process (SSIP) hypothesis was proposed to elucidate how the visual system constructs the ground-surface representation in the intermediate distance range (He et al, 2004 Perception 33 789–806). According to the hypothesis, the SSIP constructs an accurate representation of the near ground surface by using reliable near depth cues. The near ground representation then serves as a template for integrating the adjacent surface patch by using the texture gradient information as the predominant depth cue. By sequentially integrating the surface patches from near to far, the visual system obtains the global ground representation. A critical prediction of the SSIP hypothesis is that, when an abrupt texture-gradient change exists between the near and far ground surfaces, the SSIP can no longer accurately represent the far surface. Consequently, the representation of the far surface will be slanted upward toward the frontoparallel plane (owing to the intrinsic bias of the visual system), and the egocentric distance of a target on the far surface will be underestimated. Our previous findings in the real 3-D environment have shown that observers underestimated the target distance across a texture boundary. Here, we used the virtual-reality system to first test distance judgments with a distance-matching task. We created the texture boundary by having virtual grass- and cobblestone-textured patterns abutting on a flat (horizontal) ground surface in experiment 1, and by placing a brick wall to interrupt the continuous texture gradient of a flat grass surface in experiment 2. In both instances, observers underestimated the target distance across the texture boundary, compared to the homogeneous-texture ground surface (control). Second, we tested the proposal that the far surface beyond the texture boundary is perceived as slanted upward. For this, we used a virtual checkerboard-textured ground surface that was interrupted by a texture boundary. We found that not only was the target distance beyond the texture boundary underestimated relative to the homogeneous-texture condition, but the far surface beyond the texture boundary was also perceived as relatively slanted upward (experiment 3). Altogether, our results confirm the predictions of the SSIP hypothesis.

Children's tactual, visual, and cross-modal transfer abilities for texture were investigated in a delayed matching-to-sample paradigm. Transfer performance from vision to touch was found to increase between 5 and 8 years of age, whereas transfer performance from touch to vision did not vary with age and matched touch-to-touch performance. Asymmetrical cross-modal abilities were observed at the age of 8 years, vision-to-touch transfer performance being higher than touch-to-vision transfer performance (experiment 2). This developmental pattern could not be attributed to limitations in the tactual or visual discriminability of the textures or to differences in tactual or visual memory between the two age groups (experiment 1). It is suggested that the increase with age in vision-to-touch performance may be related to the intervention of more efficient top – down perceptual processes in the older children.

Change blindness (CB) occurs when people miss changes across views. Hypothetically, CB would occur if observers failed to represent information about the changing object, but CB would also occur if observers represented and failed to compare information across views, or represented only the pre- or post-change object. For a variety of reasons, previous studies have been unable to determine which of these alternatives contribute to CB in an incidental real-world setting. To address these ambiguities, we conducted two real-world experiments using stimuli that changed on only one feature and tested recognition memory for both the changing feature and a non-changing feature. Participants also provided confidence ratings on recognition responses, allowing us to test whether CB has multiple causes within a single task setting. The results suggest that, in a single real-world setting, CB can be caused by both a failure to represent and a failure to compare information across views.

The information that people use to perceive whether a tool is suitable for a certain task depends on what is available at a given time. Visually scanning a tool and wielding it each provide information about the functional attributes of the tool. In experiment 1, we investigated the relative contributions of vision and dynamic touch to perceiving the suitability of various tools for various tasks. The results show that, when both vision and dynamic touch are available, the visual information dominates. When limited to dynamic touch, ratings of suitability are constrained by the inertial properties of the tool, and the inertial properties that are exploited depend on the task. In experiment 2, we asked whether the manner in which a tool is manipulated in exploration depends on the task for which it is being evaluated. The results suggest that tools are manipulated in ways that reflect intentions to perceive particular affordances. Exploratory movements sometimes mimic performatory movements.

Gaze direction can be represented in terms not only of local-feature information (ie the location of the pupil in the eye socket), but also of an emergent property—whether the perceived gaze direction is straight or averted. To examine whether this emergent property is preferentially accessed when searching for an oddly directed gaze, we experimentally manipulated the local-feature information and the emergent property independently, in order to investigate the influences of both types of information on visual searches for an oddly directed gaze. We found that the primary determinant of search efficiency was not the local-feature information of eye region, but the emergent property—the perceived direction of the gaze. This finding is consistent with the idea that important social signals are recognised primarily by their emergent properties.

Striking changes in sensitivity to tonality across the pitch range are reported. Participants were presented a key-defining context (do-mi-do-sol) followed by one of the 12 chromatic tones of the octave, and rated the goodness of fit of the probe tone to the context. The set of ratings, called the probe-tone profile, was compared to an established standardised profile for the Western tonal hierarchy. The presentation of context and probe tones at low and high pitch registers resulted in significantly reduced sensitivity to tonality. Sensitivity was especially poor for presentations in the lowest octaves where inharmonicity levels were substantially above the threshold for detection. We propose that sensitivity to tonality may be influenced by pitch salience (or a co-varying factor such as exposure to pitch distributional information) as well as suprathreshold inharmonicity.

Gori and Stubbs (2006 Perception 35 1573–1577) have published some visual illusions elicited in observers who fixate very blurred disks while they move their head towards and away from them. We interpret these illusions as afterimages. We support this with examples of eccentric, colored, and striped afterimages.