COVERT ORIENTING OF ATTENTION IN MACAQUES .1. EFFECTS OF BEHAVIORAL CONTEXT

1. A task was used by Posner (1980) to measure shifts of attention tha t occurred covertly, in the absence of an eye movement or other orient ing response. This paradigm was used here to assess the nature of cove rt attentional orienting in monkeys to develop an animal model for neu rophysiological studies. Shifts of attention were measurable in monkey s and were consistent across a variety of experimental conditions. 2. The paradigm required that monkeys fixate and release a bar at the app earance of a target, which was preceded by a cue. Reaction times to ta rgets that followed peripheral cues at the same location (validly cued ) were significantly faster than those that followed cues in the oppos ite visual field (invalidly cued). This difference was defined as the validity effect, which as in humans, is used as the measure of a cover t attentional shift. 3. When the proportion of validly to invalidly cu ed targets was decreased, no change was seen in the validity effect of the monkeys. This is in contrast to humans, for whom the ratio of val idly to invalidly cued targets affected the magnitude of the validity effect. When 80% of the targets were preceded by cues at the same loca tion, the validity effect was greatest. The effect was reversed when t he proportions were reversed. From this result, it is concluded that c ognitive processes can affect covert orienting to peripheral cues in h umans, whereas in trained monkeys, performance was automatic. 4. To te st whether cognitive influences on attention could be demonstrated in the monkey, an animal was taught to use symbolic, foveal signals to co vertly direct attention. The magnitude of this validity effect was gre ater than that obtained with peripheral cues. 5. The effects of motiva tional and perceptual processes were tested. Although overall reaction times could. be modified, the facilitating effects of the cues persis ted. This constancy across motivational and perceptual levels supports the notion that the monkeys were performing the task in an automatic way, under the exogenous control of peripheral cues. 6. Most visual cu ing has been tested with visual landmarks at the locations of cues and targets. These monkeys were trained with such landmarks, and when tes ted without them, the attentional effect of the cues was nearly abolis hed. These data suggest that local visual features can be important fo r covert orienting. 7. To determine the spatial extent of the effect o f the cue, monkeys and humans were tested with four cue-target distanc es (0-60-degrees). Reaction times were fastest at a cue-target distanc e of 0-degrees (validly cued) for the earliest temporal interval for b oth monkeys and humans. For the monkey, the validity effect peaked at 20-degrees and declined more eccentrically. For humans, the validity e ffect was qualitatively similar for distances from 20 to 60-degrees. 8 . The present studies demonstrate that peripheral visual cues result i n attentional shifts in monkeys, similar to those described in humans. This approach provides an animal model for exogenously elicited atten tional shifts. The effects of peripheral cues are reliable in trained monkeys and are minimally susceptible to endogenous or experimental in fluences. However, like humans, monkeys can exert endogenous control o ver the covert orienting of attention when symbolic cues are used.