Neuroscience 2002 Abstract
| Presentation Number: | 657.10 |
|---|---|
| Abstract Title: | Gain control in macaque area MT is directionally selective. |
| Authors: |
Rust, N. C.*1
; Majaj, N. J.1
; Simoncelli, E. P.1
; Movshon, J. A.1
1Center for Neural Science, New York University, New York, NY |
| Primary Theme and Topics |
Sensory Systems - Vision -- Extrastriate visual cortex: Motion and depth |
| Session: |
657. Visual cortex: motion II Poster |
| Presentation Time: | Wednesday, November 6, 2002 9:00 AM-10:00 AM |
| Location: | Hall A2-B3 F-55 |
| Keywords: | MT, gain control, opponent inhibition |
In models of the response of V1 and MT cells, the gain control signal is taken to be the pooled activity of nearby cells of all direction and orientation preferences (Heeger, 1992; Simoncelli & Heeger, 1998), but the promiscuity of this inhibition has not been directly tested. We studied the stimulus specificity of this signal in MT cells by comparing responses to drifting test gratings presented alone with those measured in the presence of a drifting pedestal grating. Targets were presented at two equally effective locations within the receptive field, and could be either superimposed or separated.
When the pedestal grating drifted in the preferred direction of the cell, responses to the test gratings were strongly reduced by the pedestal, regardless of whether the test and pedestal were separated or superimposed. These results support previous work suggesting gain control acts globally over MT receptive fields (Britten & Heuer, 1999; Majaj et al, SFN 2000). When the pedestal grating drifted in the null direction, test responses were reduced only when the test grating was superimposed on the pedestal and were largely unaffected when the gratings were separated. The difference between the results obtained with masks moving in the preferred and null directions suggests that gain control in MT is tuned for the direction of motion.
Moreover, the existence of a tuned normalization signal in MT that follows an untuned normalization stage in V1 may describe the phenomenon of local motion opponency (Qian et al. 1994) without the need to invoke an explicit opponent computation.
When the pedestal grating drifted in the preferred direction of the cell, responses to the test gratings were strongly reduced by the pedestal, regardless of whether the test and pedestal were separated or superimposed. These results support previous work suggesting gain control acts globally over MT receptive fields (Britten & Heuer, 1999; Majaj et al, SFN 2000). When the pedestal grating drifted in the null direction, test responses were reduced only when the test grating was superimposed on the pedestal and were largely unaffected when the gratings were separated. The difference between the results obtained with masks moving in the preferred and null directions suggests that gain control in MT is tuned for the direction of motion.
Moreover, the existence of a tuned normalization signal in MT that follows an untuned normalization stage in V1 may describe the phenomenon of local motion opponency (Qian et al. 1994) without the need to invoke an explicit opponent computation.
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2002 Neuroscience Meeting Planner. Orlando, FL: Society for Neuroscience, 2002. Online.
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