RESPONSES OF INTRAPARIETAL NEURONS TO SACCADIC TARGETS AND VISUAL DISTRACTORS

Current evidence suggests that neuronal activity in the lateral intrap arietal area (LIP) reflects sensory-motor processes, but it, remains u nclear whether LIP activation participates directly in the planning of future eye movements or encodes data about both sensory events and th e behavioral significance of those sensory events. To examine this iss ue, 31 intraparietal neurons were studied in awake, behaving monkeys t rained to perform two tasks that independently controlled the location of a saccadic target and the location and behavioral relevance of a v isual distractor. In both of these tasks, two eccentric light-emitting diodes (LEDs) were illuminated yellow, one above and one below a fixa tion stimulus. Shortly after the eccentric LEDs were illuminated. a ch ange in the color of the fixation stimulus indicated which of these LE Ds served as the saccadic goal and which served as a visual distracter . In the first or distractor-irrelevant task, fixation offset indicate d that the subject must initiate a saccade shifting gaze to the saccad ic goal. In the second or distractor-relevant task, distracter offset served as the saccade initiation cue. Intraparietal neurons responded more strongly in association with an LED that served as a saccadic tar get than in association with the same LED when it served as a visual d istracter. Neuronal responses in association with either target or dis tracter stimuli on distractor-relevant and distractor-irrelevant block s of trials were statistically indistinguishable. When the location of either the target or the distracter was varied across trials, the res ponse of each neuron in association with a particular stimulus locatio n was always greater for targets than for distracters and the magnitud e of this response difference was independent of distracter relevance; however, distracters were nearly always associated with some intrapar ietal neuronal activity. A target/distractor selectivity index was com puted for each neuron as the difference between responses associated w ith targets minus responses associated with distracters divided by the sum of these values. When the selectivity of each neuron on the distr actor-relevant task was plotted against the selectivity of the same ne uron on the distractor-irrelevant task, activity in the population of intraparietal neurons was found to be independent of distracter releva nce. These data suggest that LIP neuronal activation represents saccad ic targets and, at a lower level of activity, visual distracters, but does not encode the relevance of distracter stimuli on these tasks.