M J Riddoch

On the Links between Visual Knowledge and Naming: a Single Case Study of a Patient with a Category-specific Impairment for Living Things

Why living things, such as animals, fruit, and vegetables, can pose recognition or naming problems compared to nonliving things for certain patients has intrigued neuropsychologists for a number of years. We report a further case study of a patient (SRB) with a category-specific impairment in naming living things, which occurred in naming from vision, taste, touch, and when auditory definitions stressed the visual properties of objects. In addition, SRB was particularly poor at retrieving the perceptual attributes of living things when asked to draw from memory, make perceptual comparisons, or name associated colours. In contrast to this, SRBs performance on standard tests of semantic memory was relatively unimpaired, although when asked to give definitions about living things (and faces) he showed interference effects from visually and semantically similar exemplars from the same category. Also, the problem in naming was not necessarily confined to living things, but also occurred with faces and when no...

How to Make the Word-Length Effect Disappear in Letter-by-Letter Dyslexia Implications for an Account of the Disorder

The diagnosis of letter-by-letter (LBL) dyslexia is based on the observation of a substantial and monotonic increase of word naming latencies as the number of letters in the stimulus increases. This pattern of performance is typically interpreted as indicating that word recognition in LBL dyslexia depends on the sequential identification of individual letters. We show, in 7 LBL patients, that the word-length effect can be eliminated if words of different lengths are matched on the sum of the confusability (visual similarity between a letter and the remainder of the alphabet) of their constituent letters. Additional experiments demonstrate that this result is mediated by parallel letter processing and not by any compensatory serial processing strategy. These findings indicate that parallel processing contributes significantly to explicit word recognition in LBL dyslexia and that a letter-processing impairment is fundamental in causing the disorder.

Features, objects, action: The cognitive neuropsychology of visual object processing, 1984-2004.

We review evidence on the cognitive neuropsychology of visual object processing, from 1984–2004, dividing the work according to whether it deals with the analysis of visual features, objects, or the relations between object processing and action. Research across this period has led to (1) a more detailed analysis of disorders of feature processing and feature binding, (2) a finer-grained understanding of disorders of object recognition, how these disorders can change over time, and their relations to visual imagery, and (3) new accounts of the relations between vision and action. Cognitive neuropsychological studies have played a key part in furthering our understanding of the functional nature of object processing in the brain.

The interaction of attention and action: From seeing action to acting on perception

We discuss evidence indicating that human visual attention is strongly modulated by the potential of objects for action. The possibility of action between multiple objects enables the objects to be attended as a single group, and the fit between individual objects in a group and the action that can be performed influences responses to group members. In addition, having a goal state to perform a particular action affects the stimuli that are selected along with the features and area of space that is attended. These effects of action may reflect statistical learning between environmental cues that are linked by action and/or the coupling between perception and action systems in the brain. The data support the argument that visual selection is a flexible process that emerges as a need to prioritize objects for action.

Fractionating the binding process: neuropsychological evidence from reversed search efficiencies.

The authors present neuropsychological evidence distinguishing binding between form, color, and size (cross-domain binding) and binding between form elements. They contrasted conjunctive search with difficult feature search using control participants and patients with unilateral parietal or fronto/temporal lesions. To rule out effects of task difficulty or loss of top-down guidance of search, the authors made conjunction search easier than feature search. Despite this, parietal patients were selectively impaired at detecting conjunction targets in their contralateral field. In contrast, the parietal patients performed like the other participants with form conjunctions, with form conjunctions being easier to detect than difficult feature targets. These data indicate a qualitative difference between binding in the form domain and binding across form, color, and size, consistent with theories that propose distinct binding processes in vision.

Mu rhythm desynchronization reveals motoric influences of hand action on object recognition

We examined the effect of hand grip on object recognition by studying the modulation of the mu rhythm when participants made object decisions to objects and non-objects shown with congruent or incongruent hand-grip actions. Despite the grip responses being irrelevant to the task, mu rhythm activity on the scalp over motor and pre-motor cortex was sensitive to the congruency of the hand grip—in particular the event-related desynchronization of the mu rhythm was more pronounced for familiar objects grasped with an appropriate grip than for objects given an inappropriate grasp. Also the power of mu activity correlated with RTs to congruently gripped objects. The results suggest that familiar motor responses evoked by the appropriateness of a hand grip facilitate recognition responses to objects.

A tale of two agnosias: Distinctions between form and integrative agnosia

The performance of two patients with visual agnosia was compared across a number of tests examining visual processing. The patients were distinguished by having dorsal and medial ventral extrastriate lesions. While inanimate objects were disadvantaged for the patient with a dorsal extrastriate lesion, animate items are disadvantaged for the patient with the medial ventral extrastriate lesion. The patients also showed contrasting patterns of performance on the Navon Test: The patient with a dorsal extrastriate lesion demonstrated a local bias while the patient with a medial ventral extrastriate lesion had a global bias. We propose that the dorsal and medial ventral visual pathways may be characterized at an extrastriate level by differences in local relative to more global visual processing and that this can link to visually based category-specific deficits in processing.

Neuropsychological Evidence for Visual- and Motor-Based Affordance: Effects of Reference Frame and Object-Hand Congruence

Two experiments are reported that use patients with visual extinction to examine how visual attention is influenced by action information in images. In Experiment 1 patients saw images of objects that were either correctly or incorrectly colocated for action, with the objects held by hands that were congruent or incongruent with those used premorbidly by the patients. The images were also shown from a 1st- and 3rd-person perspective. There was an overall reduction in extinction for objects colocated for action. In addition, there was an extra benefit when the objects were held in hands congruent with those used by the patients and when the objects were seen from a 1st-person perspective. This last result fits with an effect of motor simulation, over and above a purely visual effect based on positioning objects correctly for action. Experiment 2 showed that effects of hand congruence could emerge with images depicted from a 3rd-person perspective when patients saw themselves holding the objects. The data indicate 2 effects of action information on extinction: (a) an effect of colocating objects for action, which does not depend on a self-reference frame (a visual effect), and (b) an effect sensitive to object-hand congruence, which does depend on a self-reference frame (a motor-based effect). The self-reference frame is induced when stimuli are viewed from a 1st-person perspective and when an image of the self is seen from a 3rd-person perspective. Both visual and motor-based effects of action information facilitate the spread of attention across objects.

'Who's that girl?' Prosopagnosia, person-based semantic disorder, and the reacquisition of face identification ability

Data are reported on three rehabilitation studies conducted on a patient, NE, who shows a tendency to misidentify familiar faces due to a person-based semantic disorder complicated by prosopagnosia. Therapy aimed to improve NEs ability to learn to recognise new people (Study 1), and her ability to recognise previously familiar people (Studies 2 and 3). In all studies, we contrasted therapy that targeted all of NEs difficulties simultaneously with therapy that focused on only one area. We show positive effects of therapy that targeted both the prosopagnosic and the semantic impairments. We discuss the implications for remediating prosopagnosia, semantic memory disturbance, and cognitive disorders that are due to multiple loci of impairment.

The attraction of yellow corn: reduced attentional constraints on coding learned conjunctive relations.

Physiological evidence indicates that different visual features are computed quasi-independently. The subsequent step of binding features, to generate coherent perception, is typically considered a major rate-limiting process, confined to one location at a time and taking 25 ms per item or longer (A. Treisman & S. Gormican, 1988, Feature analysis in early vision: Evidence from search asymmetries, Psychological Review, Vol. 95, pp. 15-48). We examined whether these processing limitations remain once bindings are learned for familiar objects. Participants searched for objects that could appear either in familiar or unfamiliar colors. Objects in familiar colors were detected efficiently at rates consistent with simultaneous binding across multiple stimuli. Processing limitations were evident for objects in unfamiliar colors. The advantage for the learned color for known targets was eliminated when participants searched for geometric shapes carrying the object colors and when the colors fell in local background areas around the shapes. The effect occurred irrespective of whether the nontargets had familiar colors, but was largest when nontargets had incorrect colors. The efficient search for targets in familiar colors held, even when the search was biased to favor objects in unfamiliar colors. The data indicate that learned bindings can be computed with minimal attentional limitations, consistent with the direct activation of learned conjunctive representations in vision.