The serial pattern found for conjunction visual-search tasks has been attributed to covert attentional shifts, even though the possible contributions of target location have not been considered. To investigate the effect of target location on orientation X color conjunction searches, the target's duration and its position in the display were manipulated. The display was present either until observers responded (Experiment I), for 104msec (Experiment 2), or for 62 msec (Experiment 3). Target eccentricity critically affected performance: A pronounced eccentricity effect was very similar for all three experiments; as eccentricity increased, reaction times and errors increased gradually. Furthermore, the set-size effect became more pronounced as target eccentricity increased, and the extent of the eccentricity effect increased for larger set sizes. In addition, according to stepwise regressions, target eccentricity as well as its interaction with set size were good predictors of performance. Wesuggest that these findings could be explained by spatial-resolution and lateral-inhibition factors. The serial self-terminating hypothesis for orientation X color conjunction searches was evaluated and rejected. We compared the eccentricity effect as well as the extent of the orientation asymmetry in these three conjunction experiments with those found in feature experiments (Carrasco & Katz, 1992).The roles of eye movements, spatial resolution, and covert attention in the eccentricity effect, as well as their implications, are discussed.A good deal of current research assumes that covert shifts of attention play an important role in visual-search tasks. In fact, the absence or presence of these attentional shifts has been said to characterize the nature of the search process: In the preattentive stage, search time is unaffected by the number of items in the display, search is said to be parallel, and no shifts are considered to have occurred; in the attentive stage, search time increases as a function of the number of items in the display, search is said to be serial, and shifts are considered to have taken place (e.g

Precuing an observer as to where a target is more likely to occur in a subsequent visual array can increase the detectability (d') of a target at that location. This is often attributed to the observer's increased allocation of some limited cognitive resource ("attention") to the cued location. Two experiments are reported which are difficult to interpret in this way even though they involve similar cue effects. The first involves postcuing a location well after the array but before the observer responds, so that the cue can influence the response but not the observation. The second involves precuing, but with slow sequential presentation of array elements prior to the response, so the observer need not share any limited resource while processing each element in turn. Enhanced detectability similar to that produced with precues and simultaneous presentation of elements is shown to occur in each experiment. An alternative data-limited (rather than resource-limited) interpretation of these effects is provided by a mathematical model in which the observer integrates equally noisy or degraded internal representations of the array elements, but gives more weight to cued elements in selecting a response. Theoretical parameters of the model are shown to provide separate measures of both an observer's overall sensitivity and precue effects in cost-benefit analyses of cuing data.

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