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

In Experiments 1-3, we monitored search performance as a function of target eccentricity under display durations that either allowed or precluded eye movements. The display was present either until observers responded, for 104 msec, or for 62 msec. In all three experiments an orientation asymmetry emerged: observers detected a tilted target among vertical distracters more efficiently than a vertical target among vertical distracters. As target eccentricity increased, reaction times and errors augmented, and the set size effect became more pronounced, more so for vertical than tilted targets. In Experiments 4-7, the stimulus spatial properties were manipulated: spatial frequency; size; and orientation. The eccentricity effect was more pronounced for vertical than tilted targets and for high- than low-spatial frequency targets. This effect was eliminated when either the size, the size and orientation, or the size and spatial frequency were magnified (M-cortical factor). By increasing the signal-to-noise ratio, magnification reduced the extent of both asymmetries; it aided more the detection of tilted than vertical and of high- than low-spatial frequency targets. Experiments 4-7 indicate that performance improvement in the magnified conditions was due to the specific pairing of stimulus size with retinal eccentricity and not to the larger stimulus size of the magnified conditions. We conclude that stimulus size, orientation and spatial frequency influence the extent of the eccentricity effect and the efficiency of search performance.

This article represents a case-study in the applicability of multidimensional scaling (MDS) to experimental aesthetics. MDS allows experimenters to ask observers to compare stimuli without specifying which criteria they should use. MDS plots data-the similarity judgements-in a "psychological space" whose number of dimensions reflects the number of ways the stimuli are perceived to differ. An experiment attempted to tap into the criteria used by non-specialists when viewing prints by the Dutch artist M. C. Escher, and to stUdywhether or not these criteria correspond to those Escher himself used to classify his work. Forty observers were shown every possible non-duplicate pair combination of twenty-six slides of Escher's prints, and were asked to rate the similarity of each pair, using any criteria they wished. Three dimensions were identified in this experiment ("dimensionality," "shape" and "degree of realism"). A neighborhood analysis (based on octants) suggests that observers' perceptions seem to correspond to Escher's groupings.