Efficiency of Selective Attention: Selection by Colour and Location Compared

Predictability of spatial and non-spatial target properties improves perception in the pre-saccadic interval

In a dual-task paradigm with a perceptual discrimination task and a concurrent saccade task, we examined participants' ability to make use of prior knowledge of a critical property of the perceptual target to improve discrimination. Previous research suggests that during a short time window before a saccade, covert attention is imperatively directed towards the saccade target location. Consequently, discrimination of perceptual targets at the saccade target location is better than at other locations. We asked whether the obligatory pre-saccadic attention shift prevents perceptual benefits arising for perceptual target stimuli with predictable as opposed to non-predictable properties. We compared conditions in which the color or location of the perceptual target was constant to conditions in which those properties varied randomly across trials. In addition to the expected improvements of perception at the saccade target location, we found perception to be better with constant than with random properties of the perceptual target. Thus, color or location information about an upcoming perceptual target facilitates perception even while spatial attention is shifted to the saccade target. The improvement occurred irrespective of the saccade target location, which suggests that the underlying mechanism is independent of the pre-saccadic attention shift, but alternative interpretations are discussed as well.

A demonstration of direct access to colored stimuli following cueing by color

To test whether cueing by color can affect orienting without first computing the location of the cued color, the impact of reorienting on the validity effect was examined. In Experiment 1 subjects were asked to detect a black dot target presented at random on either of two colored forms. The forms started being presented 750 ms before the onset of a central cue (either an arrow or a colored square). In some proportion of the trials the colors switched locations 150 ms after cue onset, simultaneously with target onset. The color switch was not found to retard responses following a color cue more than following a location cue. Furthermore, it did not reduce the validity effect of the color cue: Though the validity effect of the location cue was quite larger than the validity effect of the color cue, both effects were additive with the presence/absence of a color switch. In Experiment 2, subjects were rather asked to detect a change in shape of one of the colored forms. In this case, color switch was found to affect performance even less following a color cue. The fact that across experiments, color switch did not retard neither responding nor orienting selectively in the color cue condition, indicates that when attention is set to a certain color, reorienting to a new object following color switch does not require re-computing the address of the cued color. That finding is argued to embarrass a strong space-based view of visual attention.

Facilitation versus inhibition in non-spatial attribute discrimination tasks

Inhibition of Return is a delay in initiating attentional shifts to previously inspected locations. It has been explained as a mechanism to facilitate visual search of a scene by inhibiting the allocation of attention to locations that have already been examined. We (Hu, Samuel, & Chan, Journal of Experimental Psychology: General, 2010) recently demonstrated that similar processing costs can appear when a non-spatial attribute (color or shape) repeats-detection of a target stimulus was slower if the target shared color or shape with a recently presented cue. In the current study, we test whether such inhibitory effects occur for non-spatial attribute repetition when observers must make a discrimination judgment about targets. We found two independent effects: First, there was a standard location-based IOR effect-target discrimination was slower when the target appeared in the same location as a preceding cue. Second, reaction times were faster if the target's color or shape matched the cue's color or shape; this facilitation effect contrasts with both the location-based inhibition that was present in the current experiments, and with the inhibitory effect of feature repetition in our previous detection task study. The data are best accounted for by a three-factor model recently suggested by Lupiáñez (Attention and time, 2010).

Is location cueing inherently superior to color cueing? Not if color is presented early enough

A possible source for the advantage of location cueing over non-spatial cueing is that orienting attention by a location cue is feasible prior to stimulus onset, whereas that is normally not the case with orienting by a non-spatial cue. To examine how critical that source is for observing an advantage, we eliminated it: In a color-preview condition, subjects were to detect a target presented on the background of one of two differently colored circles (where color-location assignment was random). In a no-preview condition, the circles were both gray, but the target was either red or green (where color assignment was random). Cue type (location vs color) was also manipulated. The color preview in Experiment 1 (in which color onset preceded cue onset) was found helpful: Whereas a substantial disparity in validity effects of the two cue types was obtained with no preview, no significant difference was found when a color preview was introduced. The validity effects of both cue types were found to be about the same also in Experiment 2, in which color onset was exactly synchronized with cue onset, and SOA was manipulated. Furthermore, the absence of an SOA x cue type interaction indicated that the time course of the color cue validity did not lag after the time course of the location cue validity, which seems incompatible with the hypothesis that a color cue cannot affect orienting without first computing a location from it prior to cue onset. Overall, the results suggest that the time course of color cueing is not inherently different from that of location cueing once its main disadvantages are removed.

Competing Top-Down Processes in Visual Selection: Evidence That Selection by Location Is Stronger Than Selection by Color

The purpose of this study was to examine whether color and position information are functionally equivalent when observers are asked to select simultaneously on both dimensions. Observers were asked to report a letter of a given color from a given region of a briefly flashed letter array, then to report any additional letters they could recall from the stimulus set. Of the additional letters, more location letters were reported than were same-color or neutral letters. The results suggested that position information has priority over color information in top-down-guided visual selection.

Can one pay attention to a particular color?

In an array of elements whose colors vary can we selectively choose to process all the items of a particular color preferentially in relation to those of another color? We addressed this question by presenting subjects with arrays containing many elements, and recording reaction times to a luminance change of one of the elements. Half the elements had one color and the other half another color--the spatial distribution being random. In two tasks--a simple detection of this change or a choice reaction time to the polarity of the change--we found that reaction times were independent of the number of items in the array. Cuing the subjects as to the color of the target item had no significant influence on the detection task, but subjects were faster if cued for the discrimination task. A further experiment replicated these findings and examined possible costs and benefits. Our final experiment separated the roles of attentional guidance and postattentional processes by having subjects judge the orientation of the target element and varying the magnitude of the target flash that defined which element was the target. We found that this judgment was also affected by color cuing, and that the size of the effect interacted with the flash strength, suggesting that color cuing has its influence at the stage of attentional guidance. We conclude that subjects can selectively attend to items on the basis of color given the appropriate task and stimulus dynamics.