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Hyun-Ah Lee, Sang-Hun Lee; Linking perceptual motion adaptation with neural adaptation in human visual cortex. Journal of Vision 2007;7(9):739. doi: 10.1167/7.9.739.
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© ARVO (1962-2015); The Authors (2016-present)
There have been attempts to localize motion adaptation in human visual cortex using the fMRI adaptation technique. However, the presence of adaptation in an area does not necessarily mean that adaptation occurs in that area intrinsically because adaptation effects may be inherited from earlier visual areas (Krekelberg et al., 2006). To address this problem, we measured tuning curves of motion adaptation along the hierarchy of visual areas in the dorsal stream using fMRI and compared them with psychophysical tuning curves of motion adaptation.
In the fMRI experiment, we measured fMRI responses to drifting low-contrast dots (800 msec duration) of varying direction before and after adaptation to 1 minute, high-contrast dots drifting coherently. During the post-adaptation scans, top-up adaptation stimuli (4.4-s) were inserted in between test stimuli. By probing changes in response after adaptation at a range of test directions relative to the adapting direction, we obtained tuning curves of adaptation. In the psychophysical experiment, the stimuli and procedures were identical to those for the fMRI experiment except that subjects performed the 2IFC task during the test period by reporting which of two intervals contained a coherent motion signal. Psychophysical tuning curves of adaptation were derived by measuring a set of thresholds at directions relative to the adapting direction by varying the contrast and coherence of test stimuli.
The amplitude and bandwidth of fMRI tuning curves became progressively lower and broader, respectively, from the early (V1) to later visual areas (MT, MST). The psychophysical tuning curves of adaptation were better accounted for by fMRI tuning curves in MT/MST than by those in early visual areas. Our findings imply that activity of MT/MST is closely linked to perceived motion adaptation, but the adaptation effect per se in MT/MST is likely to be inherited from the early visual cortex (Rust et al., 2006).
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