Distinguishing the effects of action relations and scene context on object perception

Objects are rarely viewed in isolation, and so how they are perceived is influenced by the context in which they are viewed and their interaction with other objects (e.g., whether objects are colocated for action). We investigated the combined effects of action relations and scene context on an object decision task. Experiment 1 investigated whether the benefit for positioning objects so that they interact is enhanced when objects are viewed within contextually congruent scenes. The results indicated that scene context influenced perception of nonaction-related objects (e.g., monitor and keyboard), but had no effect on responses to action-related objects (e.g., bottle and glass) that were processed more rapidly. In Experiment 2, we reduced the saliency of the object stimuli and found that, under these circumstances, scene context influenced responses to action-related objects. We discuss the data in terms of relatively late effects of scene processing on object perception.     

Coactive processing of sensory signals for in-group but not out-group stimuli

ABSTRACT

There is ample evidence showing that decision times are shorter when detecting two targets for which the same response is required, compared to when only one of the targets is present—resulting in a redundancy gain. Though effects of perceptual manipulations on redundancy gains are established, effects of social associations are still unclear. Here, we examined for the first time whether associating arbitrary stimuli with in-group as opposed to out-group targets modulates redundancy gains. Participants made associations between a shape, a colour and either in- or out-group labels. They then had to discriminate whether in- or out-group stimuli appeared (single or redundant features). Responses to in-group but not to out-group stimuli violated predictions of models in which the associated features are processed independently, and were consistent with in-group stimuli being processed with super-capacity. Our results, replicated across two experiments, providing the first evidence that there is enhanced perceptual integration for information associated with an in-group.     

Eye movements in search in visual neglect

We report data on eye movements in a patient (MP) with unilateral visual neglect, in a task of searching a real-world scene. We demonstrate that MP missed some contralesional targets after fixating on them. On such “miss”; trials, MP's eye movements were similar to those on objects in target-absent trials trials, where MP was cued to search for a target that was not actually present. In addition, MP showed little evidence of memory for the locations of objects that remained across a trial, though poor memory fails to explain performance on trials where targets were fixated. We suggest that, in this case, neglect reflected the poor uptake of information from the contralesional side of space, so that even fixated targets sometimes failed to match a “template” held in his memory.     

Top-up search and the attentional blink: A two-stage account of the preview effect in search

An inefficient visual search task can be facilitated if half the distractor items are presented as a preview prior to the presentation of the remaining distractor items and target. This benefit in search is termed the preview effect. Recent research has found that a preview effect can still occur if the previewed items disappear before reappearing again just before the search items (the “top-up” procedure). In this paper we investigate the attentional demands of processing during the preview and the top-up periods. Experiment 1 found that if attention is withdrawn from the top-up stage then no preview effect occurs. Likewise if attention is withdrawn from the initial preview period then the preview effect is reduced (Experiment 2). The data suggest that the preview effect is dependent on attention being paid both to the initial display and also to the re-presentation of the old display before the search display appears. The data counter accounts of preview search in terms of automatic attention capture by new items or by inhibition of return. We discuss alternative accounts of the results, and in particular suggest an amalgamation of a temporal grouping and a visual marking account of preview search.     

Visual object agnosia without prosopagnosia or alexia: Evidence for hierarchical theories of visual recognition

Abstract

A single case study is presented of a patient, Mr. W, with a selective deficit in recognizing pictures and real objects, linked to impaired stored visual knowledge about objects. Despite this, Mr. W maintained a preserved ability both to read aloud printed words and to recognize famous faces, when compared with age-matched control subjects. In addition, his access to semantic information from words was superior to that from pictures. The data provide evidence that visual agnosia can occur without alexia or prosopagnosia, contrary to recent proposals (Farah 1990, 1991). This finding is consistent with a hierarchical model of visual object recognition in which agnosia can reflect impaired stored knowledge of objects without accompanying perceptual deficits. The selective recognition deficit for objects further indicates that stored knowledge concerning different classes of visual stimuli (common objects, faces, and words) is separately represented in the brain.     

The time course of preview search with color-defined, not luminance-defined, stimuli

We examined the time course of preview search, using stimuli that were defined by color, but not by luminance changes. We demonstrate that, under these conditions, search performance in a preview condition improved selectively over time, relative to a baseline condition in which all the items appeared together. The data confirm earlier reports from Humphreys, Kyllinsbaek, et al. (2004) and Watson and Humphreys (1997), who used luminance-defined stimuli and showed a long time course to preview search. The data contradict Donk and Verburg (2004), who argued that the preview benefit was instantaneous but did not include baseline conditions with which to test for any influence of distractors equivalent to the old items in preview search, even under nonpreview conditions. The data support the proposal that the prioritization of new items in preview search is a time-consuming business.     

Prioritization in visual search: visual marking is not dependent on a mnemonic search

Visual marking (VM) refers to our ability to completely exclude old items from search when new stimuli are presented in our visual field. We examined whether this ability reflects an attentional scan of the old items, possibly allowing observers to apply inhibition of return or maintain a memory representation of already seen locations. In four experiments, we compared performance in two search conditions. In the double-search (DS) condition, we required participants to pay attention to a first set of items by having them search for a target within the set. Subsequently, they had to search a second set while the old items remained in the field. In the VM condition, the participants expected the target only to be in the second (new) set. Selection of new items in the DS condition was relatively poor and was always worse than would be expected if only the new stimuli had been searched. In contrast, selection of the new items in the VM condition was good and was equal to what would be expected if there had been an exclusive search of the new stimuli. These results were not altered when differences in Set 1 difficulty, task switching, and response generation were controlled for. We conclude that the mechanism of VM is distinct from mnemonic and/or serial inhibition-of-return processes as involved in search, although we also discuss possible links to more global and flexible inhibition-of-return processes not necessarily related to search.     

Domain-specificity and theory of mind: evaluating neuropsychological evidence

Humans' unique aptitude for reasoning about mental states, known as Theory of Mind (ToM), can help explain the unique character of human communication and social interaction. ToM has been studied extensively in children, but there is no clear account of the cognitive basis of ToM in adults. Evidence from functional imaging and neuropsychology is beginning to address this surprising gap in our understanding, and this evidence is often thought to favour a domain-specific or modular architecture for ToM. We present a systematic approach to this issue for the paradigmatic case of belief reasoning, and argue that neuropsychological data provide no clear evidence for domain-specificity or modularity. Progress in understanding ToM requires new tasks that isolate potentially distinct components of this complex ability.     

Visual marking: the effects of irrelevant changes on preview search

Visual search is facilitated when participants receive a preview of half of the distractors before presentation of the second distractor set (Watson & Humphreys, 1997). In seven experiments, we examined the effects of irrelevant change on this preview benefit. Experiments 1-4 showed that the benefit was not disrupted by the abrupt appearance of irrelevant distractors during the preview period unless they were the same color as the new items. However, blinking off-and-on irrelevant distractors that were present at the start of the preview period disrupted the preview benefit irrespective of their feature overlap with other items (Experiments 5-7). The data are consistent with the inhibition of old stimuli (visual marking) via a location-based template along with an anticipatory feature-based set for new stimuli.