Unilateral left prosopometamorphopsia: A neuropsychological case study

Face distortions in prosopometamorphopsia provide new insights into the organization of face perception

Prosopometamorphopsia (PMO) is a striking condition of visual perception in which facial features appear distorted, for example drooping, swelling, or twisting. Although numerous cases have been reported, few of those investigations have carried out formal testing motivated by theories of face perception. However, because PMO involves conscious visual distortions to faces which participants can report, it can be used to probe fundamental questions about face representations. Here we review cases of PMO that address theoretical questions in visual neuroscience including face specificity, inverted face processing, the importance of the vertical midline, dissociable representations for each half of the face, hemispheric specialization, the relationship between face recognition and conscious face perception, and the reference frames that face representations are embedded within. Finally, we list and touch upon eighteen open questions that make clear how much is left to learn about PMO and the potential it has to provide important advances in face perception.

The influence of visual distortion on face recognition

A person's ability to recognise familiar faces is critical to their participation in many aspects of society. Following an acquired brain injury or retinal disease, however, faces can appear distorted, a phenomenon known as prosopometamorphopsia. Although case reports have described a variety of changes in the appearance of faces during prosopometamorphopsia, the influence of the disorder on face recognition has not been rigorously investigated. In the present report, we quantify how well healthy observers can recognise familiar faces that have been distorted using a parametric model of prosopometamorphopsia. Our results reveal that face recognition varies systematically with the parameters of visual distortion, which, importantly, interact with the size of the face in a nonlinear but highly predictable manner. Our findings demonstrate that prosopometamorphopsia can lead to a surprising range of changes in the appearance of faces. The impact of visual distortion on face recognition thus depends critically on the distance at which the face is viewed, which is likely to change across social and clinical contexts.

Lack of awareness despite complex visual processing: Evidence from event-related potentials in a case of selective metamorphopsia

Visual awareness is thought to result from integration of low- and high-level processing; instances of integration failure provide a crucial window into the cognitive and neural bases of awareness. We present neurophysiological evidence of complex cognitive processing in the absence of awareness, raising questions about the conditions necessary for visual awareness. We describe an individual with a neurodegenerative disease who exhibits impaired visual awareness for the digits 2 to 9, and stimuli presented in close proximity to these digits, due to perceptual distortion. We identified robust event-related potential responses indicating 1) face detection with the N170 component and 2) task-dependent target-word detection with the P3b component, despite no awareness of the presence of faces or target words. These data force us to reconsider the relationship between neural processing and visual awareness; even stimuli processed by a workspace-like cognitive system can remain inaccessible to awareness. We discuss how this finding challenges and constrains theories of visual awareness.

Prosopometamorphopsia and alexia following left splenial corpus callosum infarction: Case report and literature review

Background

Lesions to the posterior section of the corpus callosum, called the splenium, and the immediate area have been separately associated with perceived visual distortions of the face (prosopometamorphopsia) or difficulty reading (alexia).

Case report

This case report describes a right-handed patient who complained of prosopometamorphopsia associated with the lower part of the face and alexia following infarction of the left splenium in the corpus callosum.

Conclusions

The splenium and adjacent retrosplenial cortex facilitate the transfer of visual information and memory function between the two hemispheres of the brain and along the Papez circuit, respectively. We believe that damage to this singular area of the brain could bring about several concurrent yet disparate symptoms, such as the reported prosopometamorphopsia and alexia with this patient.

Visual disorders, the prosopometamorphopsia and prosopagnosia type in the early days after the onset of brain hemorrhagic stroke--a case report

Presented case report illustrates symptoms of prosopometamorphopsia (PM) and prosopagnosia, observed in the early days after the onset of a hemorrhagic stroke resulting from a complication of endovascular treatment of intracranial aneurysms and the use of anticoagulation therapy. PM is a visual disorder in which faces are perceived as distorted. The female patient described in the present study reported that faces she looked at seemed younger or older than in reality or as if they were dirty, swollen, or with a grimace. She also experienced symptoms of prosopagnosia, which is difficulty of recognizing familiar faces of people (e.g., of her husband and daughter). In the interview 6 months after the first examination, the patient reported spontaneous withdrawal of the visual disturbances.