Search

This study examines how brain damage can affect the cognitive processes that support the integration of sensory input and prior knowledge during shape perception. It is based on the first detailed study of acquired ventral simultanagnosia, which was found in a patient (M.T.) with posterior occipitotem-poral lesions encompassing V4 bilaterally. Despite showing normal object recognition for single items in both accuracy and response times (RTs), and intact low-level vision assessed across an exten-sive battery of tests, M.T. was impaired in object identification with overlapping figures displays. Task performance was modulated by familiarity: Unlike controls, M.T. was faster with overlapping displays of abstract shapes than with overlapping displays of common objects. His performance with overlap-ping common object displays was also influenced by both the semantic relatedness and visual similarity of the display items. These findings challenge claims that visual perception is driven solely by feedfor-ward mechanisms and show how brain damage can selectively impair high-level perceptual processes supporting the integration of stored knowledge and visual sensory input. [ABSTRACT FROM AUTHOR]

Unilateral damage to visual cortex of the parietal or occipital lobe can cause the patient to be unaware of contralesional visual information due to either hemispatial neglect or hemianopia. It is now known that both neglect and hemianopia result from the disruption of a dynamic interaction between cortical visual pathways and more phylogenetically primitive visual pathways to the midbrain. We consider the therapeutic implications of these cortical–subcortical interactions in the rehabilitation of hemianopia. We start with the pheonmenon of “blindsight”, in which patients with hemianopia can be shown, by implicit measures of visual detection or discrimination, to process visual information without conscious awareness. Some variants of blindsight have been postulated to recruit subcortical processes, while others may reflect compensatory optimisation of processing of spared visual cortex. Both mechanisms may offer opportunities for innovative strategies for rehabilitation of visual field defects. We relate the neural mechanisms that have been proposed to underlie blindsight to those that have been suggested to underlie the recovery of visual function after rehabilitation. It is suggested that the similarity and overlap of the neural processes supporting blindsight and recovery of visual function might provide insights for effective rehabilitation strategies for restoring visual functions. [ABSTRACT FROM AUTHOR]

Primary objective : To investigate the utility of feedback of brain-imaging findings as an intervention for improving impaired awareness, depression and anxiety levels. Research design and methods : A prospective within-subjects repeated measures design was used with an intervention sample of 17 adults with acquired brain injury. Baseline and post-intervention measures included self-report and questionnaire-based self-awareness instruments and self-report questionnaires for depression and anxiety. Participants also completed a range of neuropsychological tests. Intervention : The intervention consisted of a session where a Consultant Neurologist explained the findings of brain scans in terms of pathological findings and possible neurobehavioural outcome. Results : Scores on measures of unawareness and two of three mood measures decreased significantly following the intervention. This improvement was maintained at 2-week follow-up. Conclusion : Individuals with an acquired brain injury may benefit from a feedback procedure where the findings of brain scans are presented. [ABSTRACT FROM AUTHOR]

In two experiments, an inhibitory tag was activated by a peripheral cue after which a saccade was made to either the cued or, with equal probability, the uncued location. Key press RTs were measured for detecting a target that then appeared, with equal probability, either at fixation or at an eccentric location. In Experiment 1, the peripheral cue onset 400 ms before the saccade instruction, and participants therefore were obliged to inhibit a saccade towards the cue. Detection was slower at the cued location whether it appeared at, or eccentric from, fixation. In Experiment 2, the peripheral cue onset after the instruction to make the saccade but before the eyes had moved. Inhibitory tagging was again observed for targets at fixation, but the effect was smaller than for eccentric targets. These findings confirm that withdrawal of attention from a cued location is not required to generate an inhibitory tag, and that the cued locus remains inhibited even if it is subsequently attended and a saccade made to fixate it. Moreover, saccade inhibition is not sufficient to account for inhibitory tagging, although it may also engender an independent inhibitory effect. [ABSTRACT FROM AUTHOR]

Summoning attention to a peripheral location, either by a peripheral cue with the eyes fixed or when a voluntary saccade is made to it and gaze is then returned to the centre, delays detection of subsequent targets at that location compared to a location in the opposite visual field. It has been proposed that oculomotor activation generates this inhibition of return (IOR). This account presupposes that the asymmetry in detection results from inhibition at the cued location rather than facilitation at the uncued location. This has been confirmed for exogenously generated IOR. However, it has not, heretofore, been confirmed for "IOR" generated by voluntary saccades. The current study investigated whether the asymmetry in target detection, elicited either by a peripheral flash or by an eye movement generated in response to a central arrowhead, reflects facilitation at the opposite location due to the path of attentional momentum. Reaction times at the cued location were slower than reaction times at the opposite or perpendicular locations, which did not differ. Opposite facilitation due to attentional momentum requires that opposite be faster than perpendicular, which was not obtained. The results were the same whether IOR was generated by an exogenous cue or by a saccade executed endogenously to a central arrow. [ABSTRACT FROM AUTHOR]

The role of covert orienting of attention in response channel activation was examined using the flanker interference and precueing paradigms. Four experiments assessed the influence of distractors on the discrimination of a target colour patch under cueing conditions (three with non-informative, exogenous cues and one with informative, endogenous cues) that modulated attention at the flanker or target locations. Across all of the experiments, the amount of interference generated by the distractors was not modulated by the facilitation and inhibition of return induced by spatial attention precues. These results are consistent with previous reports of patients with neglect, which demonstrated that flanker interference proceeds at unattended locations (Audet, Bub, & Lecours, 1991; Cohen, Ivry, Rafal, & Kohn, 1995), and they suggest that response channel activation can occur independently from spatial attention. [ABSTRACT FROM AUTHOR]