Hemispheric asymmetries for spatial frequency discrimination in a selective attention task

Hemispheric specialization for spatial frequency processing was investigated by measuring reaction times to sinusoidal gratings in 12 healthy subjects. Stimuli of 1.5, 3, and 6 c/deg were randomly presented at two peripheral locations in the left (LVF) and right (RVF) upper visual hemifields during a selective attention task. Subjects were instructed to pay covert attention and to respond to a frequency in a given hemifield ignoring all other stimuli. Results showed that RTs were significantly faster at LVF than RVF for low frequency gratings, and at RVF than LVF for high frequency gratings. Furthermore, RTs were faster to 6 than 1.5 c/deg at the RVF, while there was not a significant difference at the LVF. In our view, these findings in a task requiring fast and accurate spatial frequency discriminations may be interpreted in terms of a hemispheric asymmetry for spatial frequency processing.