The effects of spatial attention on temporal resolution

Purpose: To better understand the temporal component of visual perception by studying the effects of spatial attention on temporal resolution. Yeshurun and Carrasco (e.g. Nature, 1998) have shown that spatial attention can sharpen spatial resolution. Here, we investigated whether this attentional mechanism can also affect temporal resolution by combining peripheral cueing with measurements of the two flash fusion threshold. Methods: Observers indicated whether the target was composed of a single continuous circle or two circles separated by a brief interval. The fusion threshold is the minimal interval between the two circles at which they are still perceived as separate circles. A trial began with a peripheral cue (50ms), which was either informative (a small bar, indicating the target location) or neutral (two horizontal lines appearing above and below the display). The informative cue allowed observers to direct their attention in advance to the target location. After a 50ms ISI the the target appeared for a total of 100ms. In the 'no-gap' condition a single circle was present for the whole duration. In the 'gap' condition two circles were presented successively, each for 45ms. The ISI between the two circles varied systematically (10-15ms), as did target eccentricity (0-16°). Results: The advanced allocation of spatial attention significantly affected observers' ability to detect the temporal gap. However, the pattern of these attentional effects on temporal resolution depended on the eccentricity at which the target appeared. Attending the target location improved performance at central locations but impaired it in the periphery. Conclusion: These results demonstrate that in addition to affecting spatial resolution, spatial attention can also affect temporal resolution. Moreover, the pattern of these effects on temporal resolution depends on the spatial position of the temporal target, and may, therefore, be a product of the attentional effects on spatial resolution.