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The Journal of Neuroscience, March 23, 2005, 25(12):3023-3031; doi:10.1523/JNEUROSCI.4476-04.2005

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Behavioral/Systems/Cognitive
The Relationship between Task Performance and Functional Magnetic Resonance Imaging Response

Giedrius T. Buracas,^1,2 Ione Fine,³ and Geoffrey M. Boynton¹

¹The Salk Institute, La Jolla, California 92037, ²Center for Functional MRI, University of California, San Diego, La Jolla, California 92093, and ³Department of Ophthalmology and Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033

We compared psychophysical and functional magnetic resonance imaging (fMRI) responses within areas V1-V3 and MT+ during both a speed and a contrast discrimination task. We found that fMRI responses did not depend significantly on task in any of these areas. Moreover, responses in V1-V3 were larger than those in MT+ for both the speed and the contrast discrimination tasks across a wide range of contrasts. This pattern of results demonstrates that localizing function based on finding those regions of cortex that show greater activity to a given task-stimulus combination than to other tasks and stimuli may, under certain conditions, be misleading. However, a simple ideal observer model assuming that perceptual thresholds are dependent on neuronal population responses does successfully show that V1 has neuronal properties consistent with our subjects' contrast discrimination performance, and that MT+ has neuronal properties consistent with subjects' performance on a speed discrimination task.

Key words: attention; contrast; speed; motion; fMRI; task

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Received Oct 31, 2004; revised February 5, 2005; accepted February 6, 2005.

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