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Clinical Trial
. 2014 Mar 19;9(3):e92284.
doi: 10.1371/journal.pone.0092284. eCollection 2014.

Why do we move our head to look at an object in our peripheral region? Lateral viewing interferes with attentive search

Ryoichi Nakashima  1 , Satoshi Shioiri  1
Affiliations
Clinical Trial

Why do we move our head to look at an object in our peripheral region? Lateral viewing interferes with attentive search

Ryoichi Nakashima et al. PLoS One. .

Abstract

Why do we frequently fixate an object of interest presented peripherally by moving our head as well as our eyes, even when we are capable of fixating the object with an eye movement alone (lateral viewing)? Studies of eye-head coordination for gaze shifts have suggested that the degree of eye-head coupling could be determined by an unconscious weighing of the motor costs and benefits of executing a head movement. The present study investigated visual perceptual effects of head direction as an additional factor impacting on a cost-benefit organization of eye-head control. Three experiments using visual search tasks were conducted, manipulating eye direction relative to head orientation (front or lateral viewing). Results show that lateral viewing increased the time required to detect a target in a search for the letter T among letter L distractors, a serial attentive search task, but not in a search for T among letter O distractors, a parallel preattentive search task (Experiment 1). The interference could not be attributed to either a deleterious effect of lateral gaze on the accuracy of saccadic eye movements, nor to potentially problematic optical effects of binocular lateral viewing, because effect of head directions was obtained under conditions in which the task was accomplished without saccades (Experiment 2), and during monocular viewing (Experiment 3). These results suggest that a difference between the head and eye directions interferes with visual processing, and that the interference can be explained by the modulation of attention by the relative positions of the eyes and head (or head direction).

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Experimental setup.
Each figure represents an eye direction condition (left, front, right). Thick arrows indicate the head (and body) orientation of the participant, and dashed arrows indicate eye direction.
Figure 2
Figure 2. Examples of stimuli.
Examples of visual search displays of (a) serial search (a spatial configuration search with T/L task) and (b) parallel search (a feature search with T/O task). There were three stimulus configuration conditions in each task: 4-corner (left), 4-center (center), and set size 16 (right).
Figure 3
Figure 3. Results of Experiment 1.
RT for correct-response trials by task for (a) serial search (i.e., T/L task) and (b) parallel search (i.e., T/O task) in Experiment 1. Error bars indicate standard errors.
Figure 4
Figure 4. Results of Experiment 3.
RT for correct-response trials by eye direction and eye condition in Experiment 3, collapsed over the viewing distance conditions. Error bars indicate standard errors.
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Grants and funding

This study was partially supported by the Core Research for Evolutional Science and Technology (CREST) Program of the Japan Science and Technology Agency (JST) to RN and SS, and by JSPS KAKENHI Grant Number 25780441 to RN. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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