Temporal synchrony in perceptual grouping: a critique

It has been hypothesized that the human visual system can use temporal synchrony for the perceptual grouping of image regions into unified objects, as proposed in some neural models. It is argued here, however, that previous psychophysical evidence for this hypothesis is due to stimulus artifacts, and that earlier studies do not, therefore, support the claims of synchrony-sensitive grouping mechanisms or processes.     

Anomalous ductile-brittle fracture behaviour in fcc crystals

The fracture behaviour of fcc crystals has been investigated by numerically simulating the dynamical failure of a three-dimensional notched crystal using molecular dynamics, simple interatomic potentials for a rare-gas solid and system sizes of about ten million atoms. We find that the solid fails by brittle cleavage for cracking on a {110} face growing in a [110]direction and by ductile plasticity for cracking on a {111} face growing in a [110]direction. Comparison of equilibrium surface energies on the crack face and Schmid factors on the primary slip systems indicates that the classical theories of fracture give predictions in contradiction with the simulation results. A hyperelasticity model is proposed to explain this discrepancy. This anomalous fracture behaviour of fcc crystals has a profound implication on general modelling of dynamic failure of solids.     

How Initial Fixation Position Influences Visual Word Recognition: A Comparison of French and Arabic

The position the eye initially fixates in a written word influences the ease with which this word is recognized. Prior research has shown that the function relating ease of word recognition and initial fixation position in the word is not symmetric. Word recognition is generally superior when the initial fixation is left rather than right of the center of the word. This asymmetry in the function relating initial fixation position to word identifiability could be due to (a) hemispheric specialization, (b) reading habits, or (c) variations in lexical constraint. The present experiments tested these alternative explanations by comparing the effects of initial fixation position in prefixed and suffixed words in French and Arabic. The results show that, contrary to both the hemispheric specialization and reading habit hypotheses, the average initial fixation curves for Arabic are asymmetric neither to the left nor to the right but depend on the morphological structure of the stimuli, thus lending support to the lexical constraint hypothesis.     

Space Perception,Visual Dissonance and the Fate of Standard Representationalism

This paper argues that a common form of representationalism has trouble accommodating empirical findings about visual space perception. Vision science tells us that the visual system systematically gives rise to different experiences of the same spatial property. This, combined with a naturalistic account of content, suggests that the same spatial property can have different veridical looks. I use this to argue that a common form of representationalism about spatial experience must be rejected. I conclude by considering alternatives to this view.     

Search for a category target in clutter

An airport security worker searching a suitcase for a weapon is engaging in an especially difficult search task: the target is not well-specified, it is not salient, and it is not predicted by its context. Under these conditions, search may proceed item-by-item. In the experiment reported here we tested whether the items for this form of search are whole familiar objects. Our displays were composed of color photographs of ordinary objects, that were either uniform in color and texture (simple), or had two or more parts with different colors or textures (compound). The observer's task was to detect the presence of a target belonging to a broad category (food). We found that when the objects were presented in a sparse array, search times to find the target were similar for displays composed of simple and compound objects. But when the same objects were presented as dense clutter, search functions were steeper for displays composed of compound objects. We attribute this difference to the difficulty of segmenting compound objects in clutter: compared with simple objects, compound objects are less likely to be organized into a single object by bottom--up grouping processes. Our results indicate that while search rates in a sparse display may be determined by the number of objects, search rates in clutter are also affected by the number of object parts.     

The perception of texture on folded surfaces

Do judgments of texture similarity reflect surface texture or image texture? To find out, we had observers view a rectangular surface that was folded into three panels, much like a brochure. Each panel was textured with an oriented noise pattern and the observers' task was to determine which side panel matched the center panel in surface texture. Information about surface geometry was conveyed by binocular disparity and by the boundaries of the rectangular surface. We found that observers were often consistently wrong, selecting the texture that differed in the image and not on the surface. In sharp contrast, when observers judged the texture orientation on each panel individually, their judgments were accurate reflections of the surface texture. So even when observers can recover surface texture, their judgments of texture similarity may still be based on image texture.     

Marked referential communicative behaviours,but no differentiation of the “knowledge state” of humans in untrained pet dogs versus 1-year-old infants

The study examines whether untrained dogs and infants take their caregiver’s visual experience into account when communicating with them. Fifteen adult dogs and 15 one-year-old infants were brought into play with their caregivers with one of their own toys. The caregiver gave the toy to the experimenter, who, in different conditions, placed it either above or under one of two containers, with both the infant or dog and the caregiver witnessing the positioning; in a third condition, the caregiver left the room before the toy was placed under one of the two containers and later returned. Afterwards, for each condition, the caregiver asked the participant to indicate the location of the toy. Neither dogs nor infants—untrained to the use of the partner’s knowledge state—showed much difference of behaviour between the three conditions. However, dogs showed more persistence for most behaviours (gaze at the owner, gaze at the toy and gaze alternation) and conditions, suggesting that the situation made more demands on dogs’ communicative behaviours than on those of infants. When all deictic behaviours of infants (arm points towards the toy and gaze at the toy) were taken into account, dogs and infants did not differ. Phylogeny, early experience and ontogeny may all play a role in the ways that both species communicate with adult humans.