Monday, November 13, 2017

Blind woman cannot discriminate gender of target faces, but perceives happy, fearful or angry expressions

Affective blindsight in the absence of input from face processing regions in occipital-temporal cortex. Christopher L. Striemer, Robert L. Whitwell, Melvyn A. Goodale. Neuropsychologia,

•    Patient MC has extensive bilateral lesions to occipital and ventral-temporal cortex
•    MC is completely blind to static stimuli, but has spared motion perception
•    Despite her extensive lesions MC can discriminate between different facial emotions
•    MC cannot discriminate gender from faces, or localize targets
•    Affective blindsight does not depend on V1, or ‘face’ regions in the ventral stream

Abstract: Previous research suggests that the implicit recognition of emotional expressions may be carried out by pathways that bypass primary visual cortex (V1) and project to the amygdala. Some of the strongest evidence supporting this claim comes from case studies of “affective blindsight” in which patients with V1 damage can correctly guess whether an unseen face was depicting a fearful or happy expression. In the current study, we report a new case of affective blindsight in patient MC who is cortically blind following extensive bilateral lesions to V1, as well as face and object processing regions in her ventral visual stream. Despite her large lesions, MC has preserved motion perception which is related to sparing of the motion sensitive region MT+ in both hemispheres.

To examine affective blindsight in MC we asked her to perform gender and emotion discrimination tasks in which she had to guess, using a two-alternative forced-choice procedure, whether the face presented was male or female, happy or fearful, or happy or angry. In addition, we also tested MC in a four-alternative forced-choice target localization task. Results indicated that MC was not able to determine the gender of the faces (53% accuracy), or localize targets in a forced-choice task. However, she was able to determine, at above chance levels, whether the face presented was depicting a happy or fearful (67%, p=.006), or a happy or angry (64%, p=.025) expression. Interestingly, although MC was better than chance at discriminating between emotions in faces when asked to make rapid judgments, her performance fell to chance when she was asked to provide subjective confidence ratings about her performance. These data lend further support to the idea that there is a non-conscious visual pathway that bypasses V1 which is capable of processing affective signals from facial expressions without input from higher-order face and object processing regions in the ventral visual stream.

Keywords: blindsight; emotion; amygdala; face processing

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