Motion

Previous investigations from several labs have show that trial-to-trial variations in the firing of neurons in the middle temporal visual area (MT) are correlated with variations in the reaction times and other performance measures of monkeys doing motion detection or discrimination tasks. However, in those experiments the direction of motion was usually aligned with the preferred direction of the neuron under study, and a systematic examination of the correlation of single unit activity with behavior when the motion is presented in other directions has not been obtained. We trained a rhesus monkey in a motion detection task and recorded from 50 single units in MT while the task was performed at 8 directions relative to the preferred direction of each neuron under study. Using receiver operating characteristic (ROC) analysis we determined the ability of single neurons to predict whether the monkey would detect the stimulus on individual trials (detect probability, DP). We found that the mean DP was about 0.6 near the preferred direction and decreased with distance from the preferred direction. Mean DP was near chance (0.5) by about 90° from the preferred direction, and was less than 0.5 for the null direction. We also analyzed the trial-by-trial correlation between single-unit firing rate and the reaction time of the animal. The correlation coefficient was about -0.2 for the preferred direction and near 0 when a direction of greater than 90° from the preferred direction was used for the task. Our results imply that many neurons in MT carry signals that are correlated with the both the animal's decisions and reaction times in the motion detection task.

2005 Society for Neuroscience Poster