The role of contour polarity, objectness, and regularities in haptic and visual perception.

Regularities like symmetry (mirror reflection) and repetition (translation) play an important role in both visual and haptic (active touch) shape perception. Altering figure-ground factors to change what is perceived as an object influences regularity detection. For vision, symmetry is usually easier to detect within one object, whereas repetition is easier to detect across two objects. For haptics, we have not found this interaction between regularity type and objectness (Cecchetto & Lawson, Journal of Experimental Psychology: Human Perception and Performance, 43, 103-125, 2017; Lawson, Ajvani, & Cecchetto, Experimental Psychology, 63, 197-214, 2016). However, our studies used repetition stimuli with mismatched concavities, convexities, and luminance, and so had mismatched contour polarities. Such stimuli may be processed differently to stimuli with matching contour polarities. We investigated this possibility. For haptics, speeded symmetry and repetition detection for novel, planar shapes was similar. Performance deteriorated strikingly if contour polarity mismatched (keeping objectness constant), whilst there was a modest disadvantage for between-2objects:facing-sides compared to within-1object:outer-sides comparisons (keeping contour polarity constant). For the same task for vision, symmetry detection was similar to haptics (strong costs for mismatched contour polarity, weaker costs for between-2objects:facing-sides comparisons), but repetition detection was very different (weak costs for mismatched contour polarity, strong benefits for between-2objects:facing-sides comparisons). Thus, objectness was less influential than contour polarity for both haptic and visual symmetry detection, and for haptic repetition detection. However, for visual repetition detection, objectness effects reversed direction (within-1object:outer-sides comparisons were harder) and were stronger than contour polarity effects. This pattern of results suggests that regularity detection reflects information extraction as well as regularity distributions in the physical world.

Regularity detection by haptics and vision.

For vision, mirror-reflectional symmetry is usually easier to detect when it occurs within 1 object than when it occurs across 2 objects. The opposite pattern has been found for a different regularity, repetition. We investigated whether these results generalize to our sense of active touch (haptics). This was done to examine whether the interaction observed in vision results from intrinsic properties of the environment, or whether it is a consequence of how that environment is perceived and explored. In 4 regularity detection experiments, we haptically presented novel, planar shapes and then visually presented images of the same shapes. In addition to modality (haptics, vision), we varied regularity-type (symmetry, repetition), objectness (1, 2) and alignment of the axis of regularity with respect to the body midline (aligned, across). For both modalities, performance was better overall for symmetry than repetition. For vision, we replicated the previously reported regularity-type by objectness interaction for both stereoscopic and pictorial presentation, and for slanted and frontoparallel views. In contrast, for haptics, there was a 1-object advantage for repetition, as well as for symmetry when stimuli were explored with 1 hand, and no effect of objectness was found for 2-handed exploration. These results suggest that regularity is perceived differently in vision and in haptics, such that regularity detection does not just reflect modality-invariant, physical properties of our environment. (PsycINFO Database Record

Effects of Line Separation and Exploration on the Visual and Haptic Detection of Symmetry and Repetition.

Detection of regularities (e.g., symmetry, repetition) can be used to investigate object and shape perception. Symmetry and nearby lines may both signal that one object is present, so moving lines apart may disrupt symmetry detection, while repetition may signal that multiple objects are present. Participants discriminated symmetrical/irregular and repeated/irregular pairs of lines. For vision, as predicted, increased line separation disrupted symmetry detection more than repetition detection. For haptics, symmetry and repetition detection were similarly disrupted by increased line separation; also, symmetry was easier to detect than repetition for one-handed exploration and for body midline-aligned stimuli, whereas symmetry was harder to detect than repetition with two-handed exploration of stimuli oriented across the body. These effects of exploration and stimulus orientation show the influence of modality-specific processing rather than properties of the external world on regularity detection. These processes may, in turn, provide insights into the nature of objectness in vision and in touch.

Motion-induced blindness measured objectively.

During central fixation, a moving pattern of nontargets induces repeated temporary blindness to even salient peripheral targets: motion-induced blindness (MIB). Hitherto, behavioral measures of MIB have relied on subjective judgments. Here, we offer an objective alternative that builds on earlier findings regarding the effects of MIB on the detectability of physical target offsets. We propose a small modification of regular MIB displays: Following a variable duration (lead time), one of the targets is physically removed. Subjects are to respond immediately afterward. We hypothesize that illusory target offsets, caused by MIB, are mistaken for physical target offsets and that errors should thus increase with lead time. Indeed, for both nonsalient and salient targets, we found that detection accuracy for physical target offsets dramatically decreased with lead time. We conclude that target offset detection accuracy is a valid objective measure of MIB. With our method, effects of guessing are minimal, and the fitting of psychometric functions is straightforward. In principle, a staircase extension--for more efficient data collection--is also possible.

Forcing free fusion of stereograms.

n order to read articles that either are on stereopsis, or use stereopsis as a tool, it is virtually inescapable to learn to fuse stereograms without the help of a stereoscope or special glasses (free fusion). For a few, this is easy. For many, it is frustratingly difficult, leading some to turn their backs on stereopsis altogether. Here, we show how presenting a stereogram on a transparency-rather than on paper-with a fixation cross behind it (for uncrossed fusion), or presenting a fixation cross on a transparency with a paper stereogram behind it (for crossed fusion), can force free fusion towards greater success.