Perception

Perceived occlusion at T-junctions or illusory contours at implicit T-junctions are often modelled by using edge information without surface context. We explored the effect of closure on perceived occlusion at T-junctions. Two vertical lines separated by a gap each had six abutting horizontal lines on opposite sides forming T-junctions. These lines were either closed or not closed into pairs at the stem ends of the Ts. In experiment 1, closed T-junction stems gave a much stronger sense of occlusion at the vertical lines than unclosed ones, even though closure information was remote from the putative occlusion and local T-junction information remained constant. When the outer two T-junctions were converted to L-junctions, perceived occlusion considerably diminished. The effect of closure on illusory-contour strength for stimuli like those of experiment 1 but with the vertical lines omitted was explored in experiment 2. The two sets of horizontal lines, separated by a gap, were either closed or not closed into pairs at their outer ends. Illusory-contour strength along the vertical alignments was much greater for closed pairs. Line terminations on both sides of the gap enhanced illusory-contour strength, but whether they were collinear or not had little effect.

We explored the tension between bottom–up and top–down contributions to object recognition in a collaboration between a visual artist and a cognitive psychologist. Initial pictorial renderings of objects and animals from various viewpoints were iteratively copied, and a series of drawings that changed from highly concrete images into highly abstract images was produced. In drawing identification in which sets were shown in reverse order, participants were more accurate, more confident, and quicker to correctly identify the evolving image when it was originally displayed from a canonical viewpoint with all salient features present. In drawing identification in which images were shown in random order, more abstract images could be resolved as a result of previously identifying a more concrete iteration of the same drawing. The results raise issues about the influence of viewpoint and feature on the preservation of pictorial images and about the role of labelling in the interpretation of ambiguous stimuli. In addition, the study highlights a procedure in which visual stimuli can degrade without necessitating a substantial loss of complexity.

In their seminal study Diamond and Carey (1986, Journal of Experimental Psychology: General 115 107–117) found a larger inversion effect for dog pictures in dog experts than novices, supporting a role of visual expertise in the observation of particularly large inversion effects for faces. However, subsequent studies have provided mixed results, and very few have compared the inversion effects for faces and familiar non-face object categories. Here we tested the effect of inversion on faces and cars in car experts and novices, using a delayed matching task across viewpoint changes. Inversion affected accuracy much more for pictures of faces than of cars for both groups, with no interaction between expertise and category. However, for car experts only there was a significant correlation between the magnitude of the inversion cost in RT for car pictures and the level of expertise as measured in an independent task. These observations support the view that the particularly large inversion effect found for faces is related to expert visual processes which can be at least partially recruited to process other non-face object categories.

In previous studies we created 8 new versions of a single face: 4 differed only in the spacing among features and 4 differed in the shape of the eyes and mouth. Compared to the spacing set, results for this feature set indicated little impairment by inversion, earlier adult-like accuracy (Mondloch et al, 2002 Perception 31 553–566), and normal performance after a history of early visual deprivation from bilateral congenital cataract (Le Grand et al, 2001 Nature 410 890, 412 786). Here we addressed the possibility that this pattern might have resulted from our having inadvertently selected easily discriminated features or including some faces with make-up. We created 20 featural versions of a single female face and asked adults, 10-year-old children, and patients treated for bilateral congenital cataract to make same/different judgments for 120 pairings (half different). The results confirm that adults easily discriminate facial features, even after early visual deprivation from cataract, and that inversion has only a small effect. By the age of 10 years, children are close to, but not quite at, adult levels of accuracy. The previous findings cannot be attributed to our having inadvertently created a feature set that was unusually easy to discriminate.

When looking monocularly at a three-dimensional (3-D) Necker cube two percepts alternate: a cube and a truncated pyramid. The latter is due to a depth reversal. We studied the effect of haptic information by having participants hold the cube with their hands and explore two of its vertices. Touch reduces the likelihood of the pyramid, consistent with a multisensory view of 3-D form perception. In addition, when the hand alternates between stationary and haptic exploration, the onset of the hand movement plays a crucial role in inhibiting reversals. A temporal analysis revealed that suppression occurred within a window lasting a few seconds from motion onset. In experiment 1, we monitored eye movements and instructed participants where to fixate. Although the percept does depend on which vertex is fixated, we ruled out a role of changes of fixation as a mediating factor for the effect of motion onset. In experiment 2, we introduced a change of position of the exploring hand as a new type of transition. This type of change did not produce the same inhibition generated by the motion onset. We conclude that motion onset does not simply draw attention towards haptic information. Rather, the influence of haptics peaks briefly after new information becomes available.

In sensory substitution, the user may be directly aware of distal objects, as in everyday perception, or make explicit cognitive inferences based on an awareness of the proximal stimulation. Anecdotal evidence supports the experience of distal attribution, but so far there have been few rigorous experimental tests of the claim. In this study, blindfolded participants observed a target light using a device consisting of a finger-mounted photodiode that drives tactile vibration on the back. With the blindfold off and the target removed, participants moved a reference object to match the perceived egocentric distance of the target. Participants who were instructed to attend to the distal target improved significantly during 2 h of practice, whereas those instructed to attend to proximal variables showed no improvement. Unsigned error increased with ratings of proximal attention, but decreased with ratings of target object solidity, consistent with distal attribution. Performance transferred to the non-dominant arm and to a rotated body orientation, demonstrating that learning did not depend on a joint-specific sensorimotor relationship between target distance and arm configuration. The results experimentally confirm that distal attribution can occur in sensory substitution, based on a perceptual strategy rather than an explicit cognitive strategy. Moreover, they suggest that the informational basis for distal attribution is not a joint-specific sensorimotor relation, but a more abstract spatial invariant.

We investigated the role of visual experience and visual imagery in the processing of two-dimensional (2-D) tactile patterns. The performance of early-blind (EB), late-blind (LB), and blindfolded sighted (S) adults in the recognition of 2-D raised-line patterns was compared. We also examined whether recognition of 2-D tactile patterns depends on the type of memory strategy (eg spatial, visuo-spatial, verbal, and kinesthetic) used by EB, LB, and S participants to perform the task. Significant between-group differences in the recognition performance have not been found despite significant between-group differences in self-reported memory strategies. Recognition performance does not vary significantly with the strategy, but correlates positively with visuo-spatial imagery abilities in the S participants. These findings may be taken to suggest that the difficulties some blind people experience with tactile pictures are not due to difficulties in processing 2-D tactile patterns.

Humans can recognise human body parts haptically as well as visually. We employed a mental-rotation task to determine whether participants could adopt a third-person perspective when judging the laterality of life-like human hands. Female participants adopted either a first-person or a third-person perspective using vision (experiment 1) or haptics (experiment 2), with hands presented at various orientations within a horizontal plane. In the first-person perspective task, most participants responded more slowly as hand orientation increasingly deviated from the participant's upright orientation, regardless of modality. In the visual third-person perspective task, most participants responded more slowly as hand orientation increasingly deviated from the experimenter's upright orientation; in contrast, less than half of the participants produced this same inverted U-shaped response-time function haptically. In experiment 3, participants were explicitly instructed to adopt a third-person perspective haptically by mentally rotating the rubber hand to the experimenter's upright orientation. Most participants produced an inverted U-shaped function. Collectively, these results suggest that humans can accurately assume a third-person perspective when hands are explored haptically or visually. With less explicit instructions, however, the canonical orientation for hand representation may be more strongly influenced haptically than visually by body-based heuristics, and less easily modified by perspective instructions.

To obtain the representation of a contour, the visual system integrates fragments of a pattern. One of the ‘binding rules’ governing this process requires that a path of conjunction in which contrast polarity is preserved be followed. Here we show that this rule has a corollary: where two alternative paths compete to emerge in opposite directions, the one with greater contrast luminance is likely to prevail.

Make-up may enhance or disguise facial characteristics. The influence of wearing make-up on facial recognition could be of two kinds: (i) when women do not wear make-up and then are seen with make-up, and (ii) when women wear make-up and then are seen without make-up. A study is reported which shows that light make-up makes it easier to recognise a face, and heavy make-up makes it more difficult. Seeing initially a made-up face makes any subsequent facial recognition more difficult than initially seeing that face without make-up.