The Anatomy of Object Recognition—Visual Form Agnosia Caused by Medial Occipitotemporal Stroke

Abstract

The influential model on visual information processing by Milner and Goodale (1995) has suggested a dissociation between action-and perception-related processing in a dorsal versus ventral stream projection. It was inspired substantially by the observation of a double dissociation of disturbed visual action versus perception in patients with optic ataxia on the one hand and patients with visual form agnosia (VFA) on the other. Unfortunately, almost all cases with VFA reported so far suffered from inhalational intoxication, the majority with carbon monoxide (CO). Since CO induces a diffuse and widespread pattern of neuronal and white matter damage throughout the whole brain, precise conclusions from these patients with VFA on the selective role of ventral stream structures for shape and orientation perception were difficult. Here, we report patient J.S., who demonstrated VFA after a well circumscribed brain lesion due to stroke etiology. Like the famous patient D.

Novel Hypotheses from a Neuropsychological Case Study: Is the Visual Ventral Cortex Critical for Both Category-Generic and Category-Specific Form Perception?

“…Furthermore, this conclusion is consistent with a wealth of more recent functional imaging studies of visual form perception in healthy subjects (GrillSpector et al, 2001). However, Karnath et al (2009) present an additional neurological case, patient J.S., with a behavioral profile similar to that of D.F. but with an intact LOC and damage to the nearby ventromedial occipitotemporal area bilaterally.…”

“…Moreover, visual form processing and object apperception are likely to overlap both cognitively and anatomically within the ventral stream, and it is possible that the VVC also makes a direct contribution to visual form processing. Thus, the new evidence of Karnath et al (2009) calls into question the widely accepted view that the LOC is critical for visual form perception and, instead, suggests that the necessary substrate may lie within the VVC. Karnath et al (2009) provide two possible explanations for the divergence of patient J.S.…”

Progressive cortical visual failure associated with occipital calcification and coeliac disease with relative preservation of the dorsal ‘action’ pathway

“…Of these other patients, JS (Karnath et al, 2009) shows the most circumscribed lesion which is confined to ventral medial occipital-temporal lobe. Given that the broader lesion territory seen in patient SB (Dijkerman et al, 2004) encompasses this area, and that DF may also show subtle ventral-medial degeneration, (Karnath et al, 2009) it might be inferred that this region is critical for recovering shape and contour information for object recognition. However, the circumscribed pattern of calcification seen in the present patient indicates that more lateral areas of occipital cortex are likewise critical and that, accordingly, no single area is responsible.…”

“…Bedside testing failed to detect any evidence of dyspraxia that may account for this decline, and at age 69 she was still able to mime the use of common objects adequately. Given the patientÕs demonstrated ability to navigate, grasp/manipulate objects, and point accurately on the Aimark, at age 81 we administered two experiments based on the classic study of Milner and Goodale (1991) and more recently by Karnath et al, (2009) For each image, participants were asked whether a rectangle was absent or present. Both the patient (88% correct) and 5 age-and gender-matched controls (100% correct) performed the task accurately, producing scores that were not reliably different from one another (t(23)=2.0, p>0.05).…”

“…Subsequent frame-by-frame analysis allowed video capture of the initial point of contact between shape, thumb and index finger. As in Karnath et al (2009), a grasp line between thumb and index finger could then be digitally superimposed on the image, and by calculating the shortest perpendicular distance between the grasp line and the shapeÕs centre of mass, a deviation score (in mm) was produced for each trial. In the perceptual task, two shapes were positioned 10cm apart on the desktop.…”