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Hoi Chung Leung

Publications and source records attributed to Hoi Chung Leung.

2 recordsLinked to original sources

Neuronal representation of occluded objects in the human brain.

Occluding surfaces frequently obstruct the object of interest yet are easily dealt with by the visual system. Here, we test whether neural areas known to participate in motion perception and eye movements are regions that also process occluded motion. Functional magnetic resonance imaging (fMRI) was used to assess brain activation while subjects watched a moving ball become occluded. Areas activated during occluded motion included the intraparietal sulcus (IPS) as well as middle temporal (MT) regions analogous to monkey MT/MST. A second experiment showed that these results were not due to motor activity. These findings suggest that human cortical regions involved in perceiving occluded motion are similar to regions that process real motion and regions responsible for eye movements. The intraparietal sulcus may be involved in predicting the location of an unseen target for future hand or eye movements.

Adolescent↗

An event-related functional MRI study comparing interference effects in the Simon and Stroop tasks.

The Stroop and Simon tasks typify a class of interference effects in which the introduction of task-irrelevant stimulus characteristics robustly slows reaction times. Behavioral studies have not succeeded in determining whether the neural basis for the resolution of these interference effects during successful task performance is similar or different across tasks. Event-related functional magnetic resonance imaging (fMRI) studies were obtained in 10 healthy young adults during performance of the Stroop and Simon tasks. Activation during the Stroop task replicated findings from two earlier fMRI studies. These activations were remarkably similar to those observed during the Simon task, and included anterior cingulate, supplementary motor, visual association, inferior temporal, inferior parietal, inferior frontal, and dorsolateral prefrontal cortices, as well as the caudate nuclei. The time courses of activation were also similar across tasks. Resolution of interference effects in the Simon and Stroop tasks engage similar brain regions, and with a similar time course. Therefore, despite the widely differing stimulus characteristics employed by these tasks, the neural systems that subserve successful task performance are likely to be similar as well.

Adult↗