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.     

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 Experiment 1 found that if attention is withdrawn from the top-up stage then no preview effect occurs. Likewise if attention is withdrawn from the initial preview period then the preview effect is reduced (Experiment 2).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.     

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.     

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.     

The development of “face-space” in infancy

Valentine (1991 Valentine, T. 1991. A unified account of the effects of distinctiveness, inversion, and race in face recognition. Quarterly Journal of Experimental Psychology, 43A: 161–204. [Taylor & Francis Online] , [Google Scholar]) proposed that faces are encoded in a multidimensional “face-space”. Here, we apply this framework to the development of face processing in infancy. It is thought that faces are encoded as “regions” in the face-space, such that variations in the face input are recognized as the same face identity. In a set of studies with 4-month-olds, 7-month-olds, and adults, we addressed the question of how these “identity regions” develop. The findings indicated that they are initially broad and become narrowed with development. Our results suggest that the face-space model can usefully be applied to face processing in infancy.     

Refractory semantics in global aphasia: On semantic organisation and the Access–Storage distinction in neuropsychology

Abstract

A single case study is reported of a global aphasic patient, JM, with impaired access to semantic information which was particularly severe for the class of proper names. JM's ability to perform matching tasks with printed words and pictures to auditory words deteriorated when items were repeated, especially when the response–stimulus interval was short. Performance was also inconsistent across items. The effect of repeated testing on items generalised to other, previously untested members of the same category. Despite this, JM was able to access general semantic information about stimuli from the affected categories (e.g. to categorise boys' and girls' names), and showed good ability to access an input lexicon concerning these stimuli. There was also a close relationship between the categories affected when he was tested with pictures and printed words. We propose that JM's deficit can be attributed to his semantic system entering an abnormal refractory state once semantic access for a particular item has been achieved, and with this stage being isolated from the procedures providing access to stored lexical knowledge. Furthermore, the representations affected seem common to pictures and printed words. We discuss the implications of the results for understanding the nature of semantic representations in general and for proper names in particular, and for the distinction between access and storage deficits in neuropsychology.     

Effects of action relations on the configural coding between objects

Configural coding is known to take place between the parts of individual objects but has never been shown between separate objects. We provide novel evidence here for configural coding between separate objects through a study of the effects of action relations between objects on extinction. Patients showing visual extinction were presented with pairs of objects that were or were not co-located for action. We first confirmed the reduced extinction effect for objects co-located for action. Consistent with prior results showing that inversion disrupts configural coding, we found that inversion disrupted the benefit for action-related object pairs. This occurred both for objects with a standard canonical orientation (e.g., teapot and teacup) and those without, but where grasping and using the objects was made more difficult by inversion (e.g., spanner and nut). The data suggest that part of the affordance effect may reflect a visuo-motor response to the configural relations between stimuli. Experiment 2 showed that distorting the relative sizes of the objects also reduced the advantage for action-related pairs. We conclude that action-related pairs are processed as configurations.