Efficient saccade planning requires time and clear choices

Abstract

We use eye movements constantly to gather information. Saccades are efficient when they maximize the information required for the task, however there is controversy regarding the efficiency of eye movement planning. For example, saccades are efficient when searching for a single target (Nature, 434 (2005) 387–91), but are inefficient when searching for an unknown number of targets in noise, particularly under time pressure (Vision Research 74 (2012), 61–71). In this study, we used a multiple-target search paradigm and explored whether altering the noise level or increasing saccadic latency improved efficiency. Experiments used stimuli with two levels of discriminability such that saccades to the less discriminable stimuli provided more information. When these two noise levels corresponded to low and moderate visibility, most observers did not preferentially select informative locations, but looked at uncertain and probable target locations equally often. We then examined whether eye movements could be made more efficient by increasing the discriminability of the two stimulus levels and by delaying the first saccade so that there was more time for decision processes to influence the saccade choices. Some observers did indeed increase the proportion of their saccades to informative locations under these conditions. Others, however, made as many saccades as they could during the limited time and were unselective about the saccade goal. A clear trend that emerges across all experiments is that conditions with a greater proportion of efficient saccades are associated with a longer latency to initiate saccades, suggesting that the choice of informative locations requires deliberate planning.

Control of gaze while walking: Task structure, reward, and uncertainty

“…It may be that fixating targets may be more rewarding than resolving the uncertainty since those targets are being acted upon in the next step, selecting them and receiving a reward. Finally, Ghahghaei and Verghese (2015) noted that the effects of uncertainty become stronger as subjects have longer to make their decisions, and in our context subjects were not under time pressure. Thus, the specific experimental context and the nature of the behavioral goals may need to be taken into account when evaluating the importance of uncertainty in gaze target choice.…”

“…Uncertainty reduction as a controlling factor in gaze target selection has also been investigated by Ghahghaei and Verghese (2015) and Verghese (2012). In these investigations, subjects performed a search task in noise for multiple targets, and it was observed that subjects choose the most likely location as often as the most uncertain location.…”

“…Similarly, fixations were governed by entropy reduction in a shape discrimination task (Renninger, Verghese, & Coughlan, 2007). Subsequent work by Verghese and colleagues, however, found that observers do not select targets to minimize uncertainty in a search for multiple targets, especially when under time pressure (Ghahghaei & Verghese, 2015; Verghese, 2012). We manipulate uncertainty by having some of our objects move in some conditions.…”

Competition between salience and informational value for saccade adaptation

“…However, we consider it unlikely that the present endpoints represent a weighted average of bottom-up and top-down information. When bottomup and top-down information compete for oculomotor control, then the contribution of each is determined by the saccade latency: Early saccades are more strongly drawn toward salience, whereas later saccades are more strongly determined by behavioral goals (Schütz, Trommershäuser, & Gegenfurtner, 2012;Ghahghaei & Verghese, 2015). Moreover, in the experiment by Schütz et al (2012), participants learned to adjust their latencies in order to adjust their endpoints and maximize their outcome over the course of the experiment.…”

Optimal and human eye movements to clustered low value cues to increase decision rewards during search

“…In our current study, saccade latencies were short (171 ms mean latency in experiment 1 and 186 ms for experiment 2) but observers might have still been able to strategize their eye movements due to the presentation of the color cues 500–650 ms prior to the display of the test image (see also, Ghahghaei & Verghese, 2014). In addition, recent studies have also shown that humans can execute a suboptimal strategy when searching for multiple targets during search (Verghese, 2012 but see, Janssen & Verghese, 2013), fail to switch from a saccadic targeting strategy (Beutter et al, 2003; Findlay, 1997) to a center of mass (ideal searcher) strategy when varying the separation between two possible target locations (Morvan & Maloney, 2012), and also depart from optimality when presented with faces with uncommon optimal points of fixations (e.g., mouth, Peterson & Eckstein, 2013b).…”