In a neural population driven by a simple grating stimulus, different subpopulations are maximally informative about changes to the grating's orientation and contrast. In theory, observers should attend to the optimal subpopulation when switching between orientation and contrast discrimination tasks. Here we used source-imaged, steady-state visual evoked potentials and visual psychophysics to determine whether this is the case. Observers fixated centrally while static targets were presented bilaterally along with a cue indicating task type (contrast or orientation modulation detection) and task location (left or right). Changes in neuronal activity were measured by quantifying frequency-tagged responses from flickering "reporter" gratings surrounding the targets. To determine the orientation tuning of attentionally modulated neurons, we measured responses for three different probe-reporter angles: 0, 20, and 45 degrees . We estimated frequency-tagged cortical activity using a minimum norm inverse procedure combined with realistic MR-derived head models and retinotopically mapped visual areas. Estimates of neural activity from regions of interest centered on V1 showed that attention to a spatial location clearly increased the amplitude of the neural response in that location. More importantly, the pattern of modulation depended on the task. For orientation discrimination, attentional modulation showed a sharp peak in the population tuned 20 degrees from the target orientation, whereas for contrast discrimination the enhancement was more broadly tuned. Similar tuning functions for orientation and contrast discrimination were obtained from psychophysical adaptation studies. These findings indicate that humans attend selectively to the most informative neural population and that these populations change depending on the nature of the task.
Publication Type: Journal Article
Publication: The Journal of neuroscience : the official journal of the Society for Neuroscience, Volume 32, p.16379-90 (2012)
Keywords: Adaptation, Computer-Assisted Magnetic Resonance Imaging, Male, Mental Processes/physiology, Neurons/*physiology, Photic Stimulation, Psychological/physiology Attention/*physiology Brain Mapping Discrimination (Psychology)/physiology Electroencephalography Evoked Potentials, Psychomotor Performance/physiology, Somatosensory/physiology Evoked Potentials, Space Perception/physiology, Visual Cortex/cytology/*physiology, Visual Eye Movements/physiology Female Humans Image Processing, Visual Pathways/cytology/physiology, Young Adult