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TWK: 7th Tübingen Perception Conference
30th Jan - 1st Feb 2004
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*** Joint winner of the TWK 2004 poster prize ***Dynamic Spatial Shifts of Neuronal Receptive Fields Toward Attended Locations in Macaque Area MT
Thilo Womelsdorf & Stefan Treue (Cognitive Neuroscience Laboratory, German Primate Center, Göttingen)
Attention excerts a multiplicative modulation on sensory responses of neurons in visual cortex. This modulation is particularly strong with multiple stimuli within a neuronal receptive field (RF). This could be due to a space-based mechanism involving shrinkage and shift of the RF toward the attended location [1, 2]. Alternatively, the response could reflect gain changes in the neuron under study, leaving shape and position of the RF unchanged [3, 4]. We examined these hypothesis directly by obtaining quantitative RF profiles of macaque area MT neurons while attention was directed at different positions within the RF. Our task required spatial attention to one of three moving random dot patterns (RDPs) in order to detect a direction change of the target RDP. Two RDPs were always placed within the RF of direction-selective neurons in MT. While one of the three stimuli was attended, quantitative RF maps were obtained by recording the responses to irrelevant, moving probe RDPs briefly appearing at the intersections of a dense virtual grid covering the RF. The resulting maps reveal a systematic shift of the sensitivity profile (the RF) toward the location of attention. We did not observe a corresponding shrinkage when attention was directed inside versus outside the RF. Our results provide the first direct evidence for a dynamic change of spatial RF position with selective attention to different subregions of the RF - on a trial-by-trial basis and under identical visual stimulation and task difficulty: Attention enhances sensitivity close to the attended location and reduces it at distant position. While the spatial response weighting corresponds to a non-multiplicative modulation, the RF-shift could also result from an attentional gain mechanism acting multiplicatively on pre-synaptic neurons with smaller RFs at attended and unattended locations. The observed spatial sensitivity increase near attended locations at the single neuron level could provide the neuronal substrate for behavioral consequences of the spatial distribution of attention: Perceptual facilitation has been reported to follow a spatial gradient centered on the attended location. At the population level it reflects the additional recruitment of neuronal resources devoted to feature analysis at and near attended positions.
[1] Moran, J. and Desimone, R. (1985): Science 229, 782-784
[2] Reynolds, J.H. and Desimone, R. (1999): Neuron 24, 22-29
[3] McAdams, C.J. and Maunsell, J.H.R. (1999): J Neurosci. 19, 431-441
[4] Treue, S. and Martinez Trujillo, J.C. (1999): Nature 399, 575-579
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