WHO:	Debbie Dao , Visiting from the L.O.B.E.S. lab at Univ. Southern California.
TOPIC:	Selective Adaptation Reduces the Sensory Gain to a Narrow Range of Orientations Around the Adapted Stimuli.
ABSTRACT:	Both pre-synaptic and post-synaptic suppression have been proposed as the cellular mechanism underlying reduced neuronal sensitivity in early visual cortex following adaptation (Finlayson & Cynader, 1995; Sanchez-Vives, et al., 2000). To investigate the perceptual processes underlying selective adaptation and to distinguish between these two cellular mechanisms, we developed an external noise plus adaptation paradigm and a theoretical framework based on a noisy observer model. Observers were adapted to a grating of +45 deg, and then detected the presence of a +45 deg grating in a 2IFC procedure in the presence of external noise. Based on an analysis of full psychometric functions in multiple external noise levels and at multiple stimulus contrasts, a contrast-gain control perceptual template model (cgcPTM) was developed and tested. Adaptation translates the psychometric functions to higher contrasts without changing the form in all noise conditions. This pattern is consistent with a post-synaptic hyper-polarization mechanism of adaptation. We concluded that adapting to a grating stimulus selectively reduces sensory gain to a narrow range of the stimulus domain. In a second experiment, we measured the orientation bandwidth of adaptation. Observers performed the same 2IFC detection task in the presence of external noise with different orientation bandwidths. Nine different noise bandwidths were tested: +/- 0, 1, 5, 10, 15, 30, 45, 60, and 90 deg about the center orientation of +45 deg. Compared to performance in unadapted control conditions, adaptation led to a general elevation in threshold in all noise conditions, with greater threshold elevation in the no noise (0 noise bandwidth) condition. ?
WHEN:	1/14/2004 4:00:00 PM
WHERE:	Med Center NBA Conference Room, 5-7432

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