Do we look at objects in the same way as we read words?

With regard to eye-movement control in reading, three phenomena describe the eyes’ fixation position within words: (1) the optimal viewing position (OVP), (2) the preferred viewing location (PVL), and (3) the fixation-duration Inverted-Optimal Viewing Position (IOVP) effect (e.g., Vitu et al., 2011). First, word centre is considered to be the OVP, defined as the position within a word where refixation probability is minimal. Second, fixation positions on words are normally distributed with a mean that is typically somewhat left of word centre; the mean of the distribution is the PVL. Third, the IOVP effect refers to the finding that fixations located at word centre are longer than those falling near the edges of a word. Collectively, these findings suggest that saccade targeting in reading is word based. The present study set out to investigate related phenomena for objects in naturalistic scenes. Analyses were based on a corpus of eye-tracking data collected from 72 participants looking at 135 scenes in scene memorisation and/or aesthetic judgment tasks. Based on a subset of these data, a recent study reported a PVL close to the centre of objects (Nuthmann & Henderson, 2010). The present study extended this work in several important ways. The PVL for objects in scenes was found to be modulated by both object size and centre-based launch site distance; long launch-site distances and larger object sizes both shifted within-object fixation position distributions towards the edge of an object (the edge that is closest to the launch site). In addition, an IOVP effect for objects in scenes was found: Fixations located at object centre were longer than those falling near the edges of an object. Somewhat surprisingly, there was no refixation OVP effect for objects. Taken together, these findings lend further support to the notion of object-based saccade targeting in scenes.