Functional magnetic resonance imaging (fMRI) has revolutionized clinical brain mapping and has become the predominant functional neuroimaging technique since its original report by Belliveau and ...colleagues.1 The appeal of fMRI is attributable to several advantages that it offers over other functional neuroimaging techniques. Functional MRI is non-invasive; it is a rapid technique that offers the opportunity for repeated measurements of the same task to investigate response consistency, to compare activations across tasks, and to measure change over time.
This study examined the relationship between spatial frequency and task demands among unilateral brain injured patients, and male and female, right and left handed control subjects on facial ...recognition. Spatial skills, including facial recognition, have been studied as lateralized skills. In general, research has pointed to the role of the right cerebral hemisphere in performing these tasks. However, when certain task parameters are manipulated, a left hemisphere advantage may also be observed. Recently, spatial frequency theory has attempted to account for such contradictory results. In this model, differences in the degree of lateral preference for a visual task are attributed to the effect manipulations have on the spatial frequency composition of the stimuli as they are perceived in the cortex. Manipulations which increase the number of high spatial frequencies in a visual percept will increase the left hemisphere advantage, while manipulations which increase the low spatial frequencies will result in a right hemisphere advantage. The current study examined the interactions between spatial frequency, and task demands which may alter the critical bands of spatial frequencies, in subject populations which differ in their spatial abilities and deficits. Human faces in which either the high or the low frequencies were removed were presented to subjects in two tasks: a Match-to-Sample task and a Same-Different task. Normal control males and females, right and left handers, were compared to patients with unilateral brain lesions. Results showed while all subjects are equally adept at processing high and low frequency filtered faces, there is a significant interaction between decision type (Same or Different) and spatial frequency. Subjects made the most errors when making "Same-Low" decisions and "Different-High" decisions. The results support the theory that manipulations in task demands alter the relevent spatial frequency spectrum required to perform the task, resulting in an interaction between these variables. No significant differences were observed between right and left handers, and males and females, on this interaction. Patients with left hemisphere lesions tended to make more "Different" errors than right hemisphere lesioned patients, while the reverse effect was found for "Same" decisions. The results support the theory that lateral differences in spatial frequency analysis underline lateral asymmetries in facial recognition.
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