Visual perception and curve tracing in form and integrative agnosia

Akhtar, Nabeela (2015). Visual perception and curve tracing in form and integrative agnosia. University of Birmingham. M.Sc.

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Abstract

The work presented within this thesis has explored distinctions between form and integrative agnosia and figure ground perception in patients with dorsal and ventral extrastriate lesions. SA was distinguished as having a dorsal extrastriate lesion and a form agnosia - an impairment in coding basic aspects of shape and lesions of the dorsal extrastriate region. HJA, our case of integrative agnosia was able to code basic aspects of shape but impaired in segmenting and grouping more complex items.

SA was impaired on object recognition but showed improved performance with animate objects relative to inanimate whilst HJA showed the opposite pattern. It was suggested SA was able to make use of top-down knowledge here. HJA demonstrated intact discrimination of simple shapes but struggled to separate figure from ground on line drawings with internal detail compared with outlines consistent with poor forming of parts into wholes.

We identified curve tracing as a useful test of figure ground segmentation in these cases. SA was highly impaired on all such tasks. HJA in comparison, showed a similar pattern of performance to controls suggesting that he was serially scanning and shifting attention at a normal rate.

HJA was found to have a strong global bias to identifying the overall letter when presented with hierarchical stimuli, while SA demonstrated a strong local bias. We suggested that this could be reflect global form proving more salient to HJA compared with local form in SA and that these biases have influenced figure ground segmentation.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

Supervisor(s):