Visual processing in pure alexia: A case study

TY - JOUR

T1 - Visual processing in pure alexia

T2 - A case study

AU - Starrfelt, Randi

AU - Habekost, Thomas

AU - Gerlach, Christian

PY - 2010/2

Y1 - 2010/2

N2 - Whether pure alexia is a selective disorder that affects reading only, or if it reflects a more general visual disturbance, is highly debated. We have investigated the selectivity of visual deficits in a pure alexic patient (NN) using a combination of psychophysical measures, mathematical modelling and more standard experimental paradigms. NN's naming and categorization of line drawings were normal with regards to both errors and reaction times (RTs). Psychophysical experiments revealed that NN's recognition of single letters at fixation was clearly impaired, and recognition of single digits was also affected. His visual apprehension span was markedly reduced for letters and digits. His reduced visual processing capacity was also evident when reporting letters from words. In an object decision task with fragmented pictures, NN's performance was abnormal. Thus, even in a pure alexic patient with intact recognition of line drawings, we find evidence of a general visual deficit not selective to letters or words. This finding is important because it raises the possibility that other pure alexics might have similar non-selective impairments when tested thoroughly. We argue that the general visual deficit in NN can be accounted for in terms of inefficient build-up of sensory representations, and that this low level deficit can explain the pattern of spared and impaired abilities in this patient.

AB - Whether pure alexia is a selective disorder that affects reading only, or if it reflects a more general visual disturbance, is highly debated. We have investigated the selectivity of visual deficits in a pure alexic patient (NN) using a combination of psychophysical measures, mathematical modelling and more standard experimental paradigms. NN's naming and categorization of line drawings were normal with regards to both errors and reaction times (RTs). Psychophysical experiments revealed that NN's recognition of single letters at fixation was clearly impaired, and recognition of single digits was also affected. His visual apprehension span was markedly reduced for letters and digits. His reduced visual processing capacity was also evident when reporting letters from words. In an object decision task with fragmented pictures, NN's performance was abnormal. Thus, even in a pure alexic patient with intact recognition of line drawings, we find evidence of a general visual deficit not selective to letters or words. This finding is important because it raises the possibility that other pure alexics might have similar non-selective impairments when tested thoroughly. We argue that the general visual deficit in NN can be accounted for in terms of inefficient build-up of sensory representations, and that this low level deficit can explain the pattern of spared and impaired abilities in this patient.

U2 - 10.1016/j.cortex.2009.03.013

DO - 10.1016/j.cortex.2009.03.013

M3 - Journal article

SN - 0010-9452

VL - 46

SP - 242

EP - 255

JO - Cortex

JF - Cortex

IS - 2

ER -