On the optimal viewing position for object processing

Atten Percept Psychophys (2016) 78:602–617 DOI 10.3758/s13414-015-1025-z On the optimal viewing position for object processing Lotje van der Linden 1 & Françoise Vitu 1 Published online: 19 November 2015 # The Psychonomic Society, Inc. 2015 Abstract Numerous studies have shown that a visually presented word is processed most easily when participants initially fixate just to the left of the word's center. Fixating on this optimal viewing position (OVP) results in shorter response times and a lower probability of making additional withinword refixations (OVP effects), but also longer initialfixation durations (an inverted-OVP or I-OVP effect), as compared to initially fixating at the beginning or the end of the word. Thus, typical curves are u-shaped (or inverted-ushaped), with a leftward bias. Most researchers explain the u-shape in terms of visual constraints, and the leftward bias in terms of language constraints. Previous studies have demonstrated that (I)-OVP effects are not specific to words, but generalize to object viewing. We further investigated this by comparing the strength and (a)symmetry of (I-)OVP effects for words and objects. To this purpose, we gave participants an object- versus word-naming task in which we manipulated the position at which they initially fixated the stimulus (i.e., a line drawing or the written name of an object). Our results showed that object viewing, just as word viewing, resulted in u-shaped (I-)OVP curves. However, the effect was weaker than for words. Furthermore, for words, the curves were biased to the left, whereas they were symmetrical for objects. This might indicate that part of the (I-)OVP effect for words is language specific, and that (I-)OVP effects for objects are a purer measure of the effect of visual constraints. * Lotje van der Linden 1 Laboratoire de Psychologie Cognitive (LPC), UMR 7290, CNRS, Aix-Marseille Université, Centre St Charles, Bâtiment 9, Case D, 3 place Victor Hugo, CS 80249, 13331 Marseille cedex 03, France Keywords Eye movements . Optimal viewing position . Object identification . Refixations . Word identification . Fixation location . Fixation duration Introduction During reading, the eyes tend to land at the center of short words, and slightly to the left of the center of long words, at least for languages that are read from left to right (Rayner, 1979). Interestingly, this so-called preferred-viewing location (PVL) generalizes to visual tasks other than reading. For example, Henderson (1993) and Foulsham and Underwood (2009) showed that the eyes also preferentially land at the center of isolated objects. More recently, Nuthmann and Henderson (2010) and Foulsham and Kingstone (2013) showed similar PVL effects when objects were embedded in complex, naturalistic visual scenes. Thus, when plotting the distributions of saccadic landing positions on words or objects, on average, the peak is near the center of the stimuli. As further developed below, previous studies have shown that initial-fixation positions on isolated words, as well as on words in sentences, influence subsequent task performance and eye movements. The same is true for isolated objects, and, to some extent, for objects in scenes. The purpose of the current study was to directly compare these initial-fixation effects between isolated words and objects. We did this by experimentally manipulating where on these stimuli the participant initially fixated. The systematic comparison between objects and words aimed at further understanding the mechanisms underlying initial-fixation effects, and determining to what extent they are specific to language processing. Atten Percept Psychophys (2016) 78:602–617 The optimal viewing position for word processing The ease with which an isolated written word is processed depends on where the eyes initially fixate. In languages that are read from left to right, words are processed most efficiently when participants initially fixate at the center of the word, or just to the left of it (O’Regan, Lévy-Schoen, Pynte, & Brugaillère, 1984; for reviews see Brysbaert & Nazir, 2005; Rayner, 1998; Vitu, 2011). Such an optimal viewing position (OVP) results in faster (O’Regan & Jacobs, 1992; O’Regan et al., 1984) and more accurate (Brysbaert, Vitu, & Schroyens, 1996; Nazir, O’Regan, & Jacobs, 1991) word identification as compared to when the eyes initially fixate either extreme end of the word. Thus, plotting response times as a function of initial fixation position reveals an asymmetric u-curve that is biased to the left of the word's center. The proportion of correct responses shows the reverse pattern (i.e., an inverted ushape). We refer to these as the response-time-OVP (RT-OVP) effect, and the accuracy-OVP effect, respectively. Interestingly, initial fixation position also affects eye movements. When participants initially fixate a word's center, they make less within-word refixations than when they initially fixate one of the word's ends. Thus, when plotting refixation probability as a function of initial-fixation position, this again results in an asymmetric u-shaped curve with a slight bias to the left of the word's center. This refixation-OVP effect was initially demonstrated in an isolated word-recognition task (O’Regan & Lévy-Schoen, 1987). Many later studies demonstrated that it generalizes to natural reading (McConkie, Kerr, Reddix, Zola, & Jacobs, 1989; Nuthmann, Engbert, & Kliegl, 2005; Rayner, Sereno, & Raney, 1996), though in a weaker manner (Vitu, O’Regan, & Mittau, 1990). Fixation durations demonstrate a reverse pattern. When participants initially fixate on the optimal position, the duration of the initial fixation is longer than when participants initially fixate the extreme ends of a word. This is the case regardless of whether the initial fixation is followed by a within-word refixation or not, and results in an inverted ucurve, again with a slight bias to the left of the word's center. We refer to this as the fixation-duration inverted OVP (I-OVP) effect. Just like the refixation-OVP effect, the fixationduration I-OVP effect is observed in isolated-word paradigms (Vitu, Lancelin, & Marrier d’Unienville, 2007; see also O’Regan & Lévy-Schoen, 1987) as well as during natural reading (Hyönä & Bertram, 2011; Nuthmann et al., 2005; Vitu, McConkie, Kerr, & O’Regan, 2001). Underlying mechanisms Although RT-OVP, accuracy-OVP, refixation-OVP, and fixation-duration I-OVP effects are robust phenomena, researchers debate the mechanisms that underlie the u- (or inverted-u-)shape and the leftward asymmetry of (I-)OVP 603 curves. The asymmetry can refer to the curve's optimum being shifted to the left of the word’s center, or to the curve being lower (or higher, for the I-OVP effect) at the left part of the word. In either case, initial-viewing position effects are stronger to the right than to the left of a word's center. Visual constraints Most researchers agree that at least part of the u-s (...truncated)