Visual processing of words in a patient with visual form agnosia: A behavioural and fMRI study

Abstract

Patient D.F. has a profound and enduring visual form agnosia due to a carbon monoxide poisoning episode suffered in 1988. Her inability to distinguish simple geometric shapes or single alphanumeric characters can be attributed to a bilateral loss of cortical area LO, a loss that has been well established through structural and functional fMRI. Yet despite this severe perceptual deficit, D.F. is able to "guess" remarkably well the identity of whole words. This paradoxical finding, which we were able to replicate more than 20 years following her initial testing, raises the question as to whether D.F. has retained specialized brain circuitry for word recognition that is able to function to some degree without the benefit of inputs from area LO. We used fMRI to investigate this, and found regions in the left fusiform gyrus, left inferior frontal gyrus, and left middle temporal cortex that responded selectively to words. A group of healthy control subjects showed similar activations. The left fusiform activations appear to coincide with the area commonly named the visual word form area (VWFA) in studies of healthy individuals, and appear to be quite separate from the fusiform face area (FFA). We hypothesize that there is a route to this area that lies outside area LO, and which remains relatively unscathed in D.F.

Visual Form Perception Can Be a Cognitive Correlate of Lower Level Math Categories for Teenagers

“…A picture consisted of two simple geometric figures. Previous studies have used geometric figure discrimination to measure visual form perception (e.g., Efron, 1969 ; Milner et al, 1991 ; Cavina-Pratesi et al, 2015 ). The four line pictures were presented simultaneously for 400 ms. Each picture had horizontal and vertical visual angles of 2.8°.…”

“…Tibber et al ( 2012 ) showed that the sensitivity to the orientations of two clusters of Gabor blobs could predict math abilities, but the sensitivity to size and density could not. The visual perception tasks used in these studies, however, were mostly focused on size, color, or brightness, which are different from visual form processing (e.g., Milner et al, 1991 ; Cavina-Pratesi et al, 2015 ). Thus, these tasks might not fully measure visual form processing.…”

Visual Perception Supports Adults in Numerosity Processing and Arithmetical Performance

“…Third, patients who suffer from visual form agnosia had difficulties in the numbers and mathematical signs (Milner et al, 1991;Cavina-Pratesi et al, 2015). For example, patient DF suffers from a permanent visual form agnosia, so she cannot distinguish single alphanumeric characters or simple geometric shapes.…”

Visual Object Agnosia in Brain Lesions (Review)

“…Besides, such patients have reduced control over the accuracy of object recognition [2]. Visual object agnosia is likely to be accompanied by impaired recognition of familiar faces (prosopagnosia), less often letters and words ("pure" alexia without agraphia) [3,11].…”