How low can you go: Spatial frequency sensitivity in a patient with pure alexia

•We test contrast sensitivity for a range of spatial frequencies in a pure alexia case.•We used a sensitive and demanding psychophysical task.•Detection and categorization of all spatial frequencies were within normal range.•Pure alexia is not caused by reduced sensitivity to particular spatial frequencies.•Pure alexia is likely caused by a deficit on a higher level of visual processing. Pure alexia is a selective deficit in reading, following lesions to the posterior left hemisphere. Writing and other language functions remain intact in these patients. Whether pure alexia is caused by a primary problem in visual perception is highly debated. A recent hypothesis suggests that a low level deficit – reduced sensitivity to particular spatial frequencies – is the underlying cause. We tested this hypothesis in a pure alexic patient (LK), using a sensitive psychophysical paradigm to examine her performance with simple patterns of different spatial frequency. We find that both in a detection and a classification task, LK’s contrast sensitivity is comparable to normal controls for all spatial frequencies. Thus, reduced spatial frequency sensitivity does not constitute a general explanation for pure alexia, suggesting that the core deficit in this disorder is at a higher level in the visual processing stream.