Abstract
Studies on visual prior entry show that two stimuli presented simultaneously, or with short temporal delay, are only rarely perceived as simultaneous if one of these stimuli is attended to. If the same two stimuli are equally unattended, simultaneity is frequently perceived. The temporal profile model (Stelmach & Herdman, 1991, Journal of Experimental Psychology: Human Perception and Performance, Vol. 17(2), pp. 539-550) predicts such an impairment of simultaneity perception by attention and allows to quantify this impairment. The higher the amount of attention selectively allocated towards one of two stimuli, the less often these stimuli should be perceived as simultaneous. We tested this hypothesis in a visual prior-entry paradigm, using masked and non-masked peripheral cues for orienting attention. The amount of attentional allocation was manipulated by varying the temporal delay between cue and cued target (34 ms, 68 ms and 102 ms). Since in larger cue-target delays the cue has more time to shift attention towards its location, a higher amount of attention should be allocated towards the respective cued target. Observers judged simultaneity of two visual stimuli presented with varying temporal delays either with a temporal-order or a simultaneity-judgment task. Results supported the hypothesis that perception of simultaneity depends on the amount of attentional allocation: The larger the cue-target delay, the less frequent were the simultaneous judgments. Visibility of the cue and the judgment task had no influence on this effect. These results provide a challenge for theories on temporal (order) perception because they contradict an (implicit) assumption of most models, viz. that simultaneity should be perceived if temporal order cannot be detected and vice versa.