| Summary: | 碩士 === 國立臺灣大學 === 心理學研究所 === 91 === Selective attention plays a crucial role in the maintenance of visual short-term memory. To probe the mechanisms underlying these roles, we use functional magnetic resonance imaging (fMRI) to isolate the brain areas subserving respectively the maintenance of feature binding and the setting of selection priority by cueing.
Seven healthy, right-handed volunteers (3 female, 4 male, 21-29 years old) performed a change detection task that requires active maintenance of visual inputs. A trial began with a fixation cross for 1 s. An initial display with four colored squares then appeared for 180 ms. Following a retention interval of 900 ms, a test probe display appeared for the participants to judge whether any change occurred from the initial display. Both accuracy and reaction time were measured. Each participant completed four change detection tasks in a 2 (type of change: color change or binding change) x 2 (cueing: valid cue or no-cue) factorial design in two experimental sessions. The two experimental sessions of interest involve either an early cue (200 ms) or a late cue (800 ms) after the termination of the initial display. Two types of change involve in either color change (changes new color on probe display) or binding change (change locations of color squares on probe display). Four conditions were blocked with the order counterbalanced in a session. There were 40 experimental trials per condition for a total of 160 trials.
In Session one with early cue, activation from the right frontal lobe (middle, inferior frontal gyrus, and precentral gyrus) was prominent in the binding-no cue condition as compared to the color-no cue condition. Cueing in the binding condition showed activation in precuneus, temporal and occipital lobe. Cueing in the color condition showed activation in superior, middle frontal gyrus, and supramaginal gyrus. In Session two with late cue, activation from the right anterior cingulated cortex and superior temporal lobe bilaterally was prominent in the binding-no cue condition as compared to the color-no cue condition. We found significant activations during condition of a late cue against the binding-change condition in left precuneus, superior temporal gyrus, superior frontal gyrus and middle frontal lobe bilaterally. We contrasted trials with a late cue against the color-change condition without a cue. The brain areas including right inferior and bilateral middle frontal gyrus, right inferior temporal gyrus, left superior temporal gyrus and precuneus were activated. These results suggest that a distributed circuit network with frontal, parietal, temporal and occipital cortex involves in the working of visual short-term memory.
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