We extended the investigation of the oblique effect in two novel ways: from stimulus-driven vision to visual attention and from space to time. Participants fixated the center of briefly flashed displays that contained a temporally varying Gabor stimulus in each of the four peripheral quadrants. Across trial blocks, we manipulated which two of the four peripheral stimuli were to be selected for a simultaneity judgment. Simultaneity judgments were significantly worse for obliquely (diagonally) attended targets than for cardinally (horizontally or vertically) attended targets, despite identical retinal stimulation across all attentional conditions. The impairment in judging the simultaneity of obliquely attended targets occurred between and within lateral hemifields, despite significantly greater temporal acuity for the left hemifield. The oblique effect in simultaneity judgments disappeared when the same targets were presented without temporally varying stimuli at distractor locations-a finding that implicates selective attention. Intriguingly, the oblique effect in excluding stimuli at distractor locations also disappeared when participants viewed the original displays but attended to spatial frequency rather than to simultaneity. These findings raise the possibility of different spatial integration windows when attending to spatial versus temporal features, even when those features are co-presented in space and time.
[Show abstract][Hide abstract] ABSTRACT: Background / Purpose:
In our previous study, Gabor stimuli were presented in four corners of a screen (14.55 deg diagonally from fixation) and changed orientation synchronously or asynchronously. Two were pre-cued as targets on each trial. Participants judged whether or not the change in orientation happened simultaneously for the cued targets. Performance (d’) was significantly worse for target pairs that were diagonally rather than horizontally or vertically aligned.Here we present new data and error analyses (false alarms vs. misses) demonstrating that this oblique effect when attending to simultaneity reflects erroneously integrated information from irrelevant spatial locations. That is, the oblique effect arose from false alarms, not misses.
This excessive spatial integration for obliquely attended targets occurred between and within lateral hemifields, despite significantly greater temporal acuity (demonstrated by a significantly lower miss rate) in the left hemifield. Within-hemifield data were obtained by moving the fixation point from the center of the screen to either side, such that the stimuli on the screen fell entirely within either the left or the right hemifield.A perceptual learning experiment demonstrated that the effect was task specific: significant learning on the simultaneity task did not generalize to a task with identical displays wherein participants judged spatial frequency differences rather than simultaneity. This suggests different spatial integration windows for different attended features (simultaneity versus spatial frequency), even when those features are co-presented in space and time.
Vision Sciences Society 11th Annual Meeting 2011; 07/2011
[Show abstract][Hide abstract] ABSTRACT: Prior reports demonstrate that simultaneity is judged less precisely in the right visual field (RVF) than in the left visual field (LVF). The present psychophysical study was conducted to provide new information about why and when (i.e., the visual information stage at which) RVF deficits arise in simultaneity judgments. In Experiment 1, participants judged either the simultaneity or the relative spatial frequency of Gabor targets in the right or left hemifield while distractors were randomly absent or present. When attention was not needed to exclude distractors, signal detection theory analyses revealed an RVF simultaneity deficit with an error pattern that implicates low RVF temporal acuity, not excessive RVF neural noise. Adding attentionally demanding distractors introduced a separate, significant RVF simultaneity deficit with error patterns that implicate the inappropriate integration of temporal asynchronies from distractor locations. Neither the distractor-independent RVF acuity deficit nor the distractor-induced RVF excessive spatial integration occurred for spatial frequency discrimination at the same retinal locations. In Experiment 2, a perceptual learning procedure significantly improved RVF simultaneity judgments. The learning was task-specific but generalized to the untrained (left) visual field and to novel retinal locations. This observation implicates the simultaneity decision as the visual information stage that sets the limit on performance.
Journal of Vision 08/2012; 12(2). DOI:10.1167/12.2.1 · 2.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multiple lines of evidence indicate that visual attention's temporal properties differ between the left and right visual fields (LVF and RVF). Notably, recent electroencephalograph recordings indicate that event-related potentials peak earlier for LVF than for RVF targets on bilateral-stream rapid serial visual presentation (RSVP) identification tasks. Might this hastened neural response render LVF targets perceptually available sooner than RVF targets? If so, how might the visual system reconcile these timing differences to estimate simultaneity across the LVF and RVF? We approached these questions by presenting bilateral-stream RSVP displays that contained opposite-hemifield targets and requiring participants to judge both the targets' temporal order and simultaneity. The temporal order judgments (TOJs) revealed that participants perceived LVF targets ∼134 ms sooner than RVF targets. This LVF hastening approximates a full cycle of visual attention's canonical ∼10 Hz (∼100 ms) temporal resolution. In contrast, performance on the simultaneity task did not exhibit the LVF hastening observed on the TOJ task, despite identical retinal stimulation across the two tasks. This finding rules out a stimulus-driven "bottom-up" explanation for the task-specific behavior. Moreover, error patterns across the two tasks revealed that, within the decision stage of simultaneity judgments, participants remapped LVF targets, but not RVF targets, to a later time in the RSVP sequence. Such hemifield-specific remapping would effectively compensate for the cross-hemifield asymmetries in neural response latencies that could otherwise impair simultaneity estimates.
Journal of Vision 07/2013; 13(8). DOI:10.1167/13.8.2 · 2.39 Impact Factor
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