Tool heads prime saccades

Abstract

Tools are wielded by their handles, but a lot of information about their function comes from their heads (the action-ends). Here we investigated whether eye saccadic movements are primed by tool handles, or whether they are primed by tool heads. We measured human saccadic reaction times while subjects were performing an attentional task. We found that saccades were executed quicker when performed to the side congruent with the tool head, even though "toolness" was irrelevant for the task. Our results show that heads are automatically processed by the visual system to orient eye movements, indicating that eyes are attracted by functional parts of manipulable objects and by the characteristic information these parts convey.

Figure 1

(A) Schematic depiction of a trial timeline for (B) head- and (C) handle-congruent saccades. See also Supplement 2 for an example timeline for oblique objects. (D) Example objects used in the experiment. (E) The saccade detection algorithm performance over an exemplary “green” trial timeline. The vertical bars denote epoch on/offsets (see labels), The green line is eye position X in screen coordinates plotted against time. Red crosses mark saccade onsets. Black cross denotes the onset of the saccade that was later taken for analysis. Figure created with Inkscape v. 0.92 (inkscape.org).

Figure 2

(A) Saccadic reaction times across conditions where saccades were congruent with the head (orange), the handle (green) and for control items (blue). Saccades executed towards the side congruent with head had significantly shorter latencies than those towards handle and control items. (B) There was no difference in the size of saccadic errors across both main experimental conditions (“Head” and “Handle). Both main conditions yielded saccades significantly more precise than in control condition. (C) Saccadic latencies for the main conditions plotted separately across all four SOAs. All error bars represent SEM. Figure created with Inkscape 0.92 (inkscape.org).