VSS 2012 abstracts, and Open satellite

Below are research presentations I’m involved in for Vision Sciences Society in May. If you’re attending VSS, don’t forget about the Publishing, Open Access, and Open Science satellite which will be Friday at 11am. Let us know your opinion on the issues and what should be discussed here

Splitting attention slows attention: poor temporal resolution in multiple object tracking

Alex O. Holcombe, Wei-Ying Chen

Session Name: Attention: Tracking (Talk session)

Session Date and Time: Sunday, May 13, 2012, 10:45 am – 12:30 pm

Location: Royal Ballroom 4-5

When attention is split into foci at disparate locations, the minimum size of the selection focus at each location is larger than if only one location is targeted (Franconeri, Alvarez, & Enns, 2007)- splitting attention reduces its spatial resolution. Here we tested temporal resolution and speed limits. STIMULUS. Three concentric circular arrays (separated by large distances to avoid spatial interactions between them) of identical discs were centered on fixation. Up to three discs (one from each ring) were designated as targets. The discs orbited fixation at a constant speed, occasionally reversing direction. After the discs stopped, participants were prompted to report the location of one of the targets. DESIGN. Across trials, the speed of the discs and the number in each array was varied, which jointly determined the temporal frequency. For instance, with 9 objects in the array, a speed of 1.1 rps would be 9.9 Hz. RESULTS. With only one target, tracking was not possible above about 9 Hz, far below the limits for perceiving the direction of the motion, and consistent with Verstraten, Cavanagh, & LaBianca (2000).  The data additionally suggest a speed limit, with tracking impossible above 1.8 rps, even when temporal frequency was relatively low. Tracking two targets could only be done at lower speeds (1.4 rps) and lower temporal frequencies (6 Hz). This decrease is approximately that predicted if at high speeds and high temporal frequencies, only a single target could be tracked. Tracking three yielded still lower limits. Little impairment was seen at very slow speeds, suggesting these results were not caused by a reduction in spatial resolution. CONCLUSION.  Splitting attention reduces the speed limits and the temporal frequency limits on tracking. We suggest a parallel processing resource is split among targets, with less resource on a target yielding poorer spatial and temporal precision and slower maximum speed.

A hemisphere-specific attentional resource supports tracking only one fast-moving object.

Wei-Ying Chen & Alex O. Holcombe

Session Name: Attention: Tracking (Talk session)

Session Date and Time: Sunday, May 13, 2012, 10:45 am – 12:30 pm

Location: Royal Ballroom 4-5

Playing a team sport or taking children to the beach involves tracking multiple moving targets. Resource theory asserts that a limited resource is divided among targets, and performance reflects the amount available per target. Holcombe and Chen (2011) validated this with evidence that tracking a fast-moving target depletes the resource. Using slow speeds Alvarez and Cavanagh (2005) found the resource consumed by additional targets is hemisphere-specific. They didn’t test the effect of speed, and here we tested whether speed also depletes a hemisphere-specific resource. To put any speed limit cost in perspective, we modeled a “total depletion” scenario- the speed limit cost if at high speeds one could not track the additional target at all and had to guess one target. Experiment 1 found that the speed limit for tracking two targets in one hemifield was similar to that predicted by total depletion, suggesting that the resource was totally depleted. If the second target was instead placed in the opposite hemifield, little decrement in speed limit occurred. Experiment 2 extended this comparison to tracking two vs. four targets. Compared to the speed limit for tracking two targets in a single hemifield, adding two more targets in the opposite hemifield left the speed limit largely unchanged. However starting with one target in both the left and right hemifields, adding another to each hemifield had a severe cost similar to that of the total depletion model. Both experiments support the theory that an object moving very fast exhausts a hemisphere-specific attentional tracking resource.

Attending to one green item while ignoring another: Costly, but with curious effects of stimulus arrangement

Shih-Yu Lo & Alex O. Holcombe

Session Name: Attention: Features I (Poster session)

Session Date and Time: Monday, May 14, 2012, 8:15 am – 12:15 pm

Location: Vista Ballroom

Splitting attention between targets of different colors is not costly by itself. As we found previously, however, monitoring a target of a particular color makes one more vulnerable to interference by distracters that share the target color. Participants monitored the changing spatial frequencies of two targets of either the same (e.g., red and red) or different colors (e.g., red and green). The changing stimuli disappeared without warning and participants reported the final spatial frequency of one of the targets. In the different-colors condition, a large cost occurs if a green distracter is superposed on the red target in the first location and a red distracter is superposed on the green target in the second location. This likely reflects a difficulty with attending to a color in one location while ignoring it in another. Here we focus on a subsidiary finding regarding perceptual lags. Participants reported spatial frequency values from the past rather than the correct final value, and such lags were greater in the different-colors condition. This “perceptual lag” cost was found when the two stimuli were horizontally arrayed but not, curiously, when they were vertically arrayed. Arrangement was confounded however with processing by separate brain hemispheres (opposite hemifields). In our new study, we unconfounded arrangement and presentation in separate hemifields with a diagonal condition- targets were not horizontally arrayed but were still presented to different hemifields. No significant different-colors lag cost was found in this diagonal arrangement (5 ms) or in the vertical arrangement (86 ms), but the cost (167 ms) was significant in the horizontal arrangement, as in previous experiments. Horizontal arrangement apparently has a special effect apart from the targets being processed by different hemispheres. To speculate, this may reflect sensitivity to bilateral symmetry and its violation when the target colors are different.

Dysmetric saccades to targets moving in predictable but nonlinear trajectories

Reza Azadi, Alex Holcombe, and Jay Edelman

Poster

A saccadic eye movement to a moving object requires taking both the object’s position and velocity into account. While recent studies have demonstrated that saccades can do this quite well for linear trajectories, its ability to do so for stimuli moving in more complex, yet predictable, trajectories is unknown. With objects moving in circular trajectories, we document failures of saccades not only to compensate for target motion, but even to saccade successfully to any location on the object trajectory. While maintaining central fixation, subjects viewed a target moving in a circular trajectory at an eccentricity of 6, 9, or 12 deg for 1-2 sec. The stimulus orbited fixation at a rate of 0.375, 0.75, or 1.5 revolutions/sec. The disappearance of the central fixation point cued the saccade. Quite unexpectedly, the circularly moving stimuli substantially compromised saccade generation. Compared with saccades to non-moving targets, saccades to circularly moving targets at all eccentricities had substantially lower amplitude gains, greater curvature, and longer reaction times. Gains decreased by 20% at 0.375 cycles/sec and more than 50% at 1.5 cycles/sec. Reaction times increased by over 100ms for 1.5 cycles/sec. In contrast, the relationship between peak velocity and amplitude was unchanged. Given the delayed nature of the saccade task, the system ought to have sufficient time to program a reasonable voluntary saccade to some particular location on the trajectory. But, the abnormal gain, curvature, and increased reaction time indicate that something else is going on. The successive visual transients along the target trajectory perhaps engage elements of the reflexive system continually, possibly engaging vector averaging processes and preventing anticipation. These results indicate that motor output can be inextricably bound to sensory input even during a highly voluntary motor act, and thus suggest that current understanding of reflexive vs. voluntary saccades is incomplete.

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