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Abstract:
Temporal patterning of stimuli can affect performance and be critical for perceptual learning. We studied the neural correlates of trial history effects using a task in which detection time was influenced by target history. Using an MRI scanner we measured BOLD signal changes while 12 subjects were presented with streams of stimuli of variable colors, shapes, and motion directions. Participants had to attend to all 3 stimulus dimensions simultaneously to report targets consisting of unpredictable stimulus feature repetitions.
Response times for targets in each stimulus dimension decreased exponentially with the number of successive targets and were well explained by a leaky integrator of target history with fast exponential decay (half-life = 1.21 trials).
Significant BOLD responses (random-effects analysis over 12 subjects, threshold = p<0.05 corrected for family-wise errors at the cluster level for all reported effects) predicted by theoretical neuronal activity reflecting the leaky integrator output for all stimulus dimensions were found bilaterally in the striatum (putamen, head and body of caudate). In addition, significant BOLD signal increases were observed in response to detected targets of any stimulus dimension in lateral occipital cortex and fusiform gyri bilaterally, with specific responses in regions compatible with area MT for motion targets, with area LO for shape targets and with area V4v for color targets.
Our behavioural data show that detected targets induce a benefit in response time for subsequent targets in the same stimulus dimension, that this acceleration effect is short-lived and can be modelled by a leaky integrator of target history. Our fMRI data show 1) BOLD signal increases compatible with neural activity reflecting the leaky integrator signals in striatum, in line with a role of the striatum in guiding motor behaviour in response to sensory cues and 2) BOLD signal increases in extrastriate visual areas in response to detected targets, reflecting immediate sensory consequences of detected targets.
