Low- and high-level first-order random-dot kinematograms: evidence from fMRI.
Maximum motion displacement (Dmax) represents the largest dot displacement in a random-dot kinematogram (RDK) at which direction of motion can be discriminated. Direction discrimination thresholds for maximum motion displacement (Dmax) are not fixed but are stimulus dependent. For first-order RDKs, Dmax is larger as dot size increases and/or dot density decreases. Dmax may be limited by the receptive field size of low-level motion detectors when the dots comprising the RDK are small and densely spaced. With RDKs of increased dot size/decreased dot density, however, Dmax exceeds the spatial limits of these detectors and is likely determined by high-level feature-matching mechanisms. Using functional MRI, we obtained greater activation in posterior occipital areas for low-level RDKs and greater activation in extra-striate occipital and parietal areas for high-level RDKs. This is the first reported neuroimaging evidence supporting proposed low-level and high-level models of motion processing for first-order random-dot stimuli.
Ho
Cindy S
CS
Department of Psychology, University of British Columbia, Canada. cindyh@interchange.ubc.ca
Giaschi
Deborah E
DE
D000293:Adolescent; D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009483:Neuropsychological Tests; D009903:Optical Illusions; D011601:Psychophysics; D012684:Sensory Thresholds; D012858:Size Perception / Q000502:physiology; D055815:Young Adult