Reading Direction and the Central Perceptual Span in Urdu and English Kevin B. Paterson*, Victoria A. McGowan, Sarah J. White, Sameen Malik, Lily Abedipour, Timothy R. Jordan College of Medicine, Biological Sciences and Psychology, University of Leicester, Leicester, United Kingdom Abstract Background: Normal reading relies on the reader making a series of saccadic eye movements along lines of text, separated by brief fixational pauses during which visual information is acquired from a region of text. In English and other alphabetic languages read from left to right, the region from which useful information is acquired during each fixational pause is generally reported to extend further to the right of each fixation than to the left. However, the asymmetry of the perceptual span for alphabetic languages read in the opposite direction (i.e., from right to left) has received much less attention. Accordingly, in order to more fully investigate the asymmetry in the perceptual span for these languages, the present research assessed the influence of reading direction on the perceptual span for bilingual readers of Urdu and English. Methods and Findings: Text in Urdu and English was presented either entirely as normal or in a gaze-contingent moving- window paradigm in which a region of text was displayed as normal at the reader’s point of fixation and text outside this region was obscured. The windows of normal text extended symmetrically 0.5u of visual angle to the left and right of fixation, or asymmetrically by increasing the size of each window to 1.5u or 2.5u to either the left or right of fixation. When participants read English, performance for the window conditions was superior when windows extended to the right. However, when reading Urdu, performance was superior when windows extended to the left, and was essentially the reverse of that observed for English. Conclusion: These findings provide a novel indication that the perceptual span is modified by the language being read to produce an asymmetry in the direction of reading and show for the first time that such an asymmetry occurs for reading Urdu. Citation: Paterson KB, McGowan VA, White SJ, Malik S, Abedipour L, et al. (2014) Reading Direction and the Central Perceptual Span in Urdu and English. PLoS ONE 9(2): e88358. doi:10.1371/journal.pone.0088358 Editor: Denis G. Pelli, New York University, United States of America Received September 16, 2013; Accepted November 26, 2013; Published February 25, 2014 Copyright: ß 2014 Paterson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: These authors have no support or funding to report. Competing Interests: Kevin Paterson is a PLOS ONE Editorial Board member. He also confirms that this does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials. * E-mail: [email protected] Introduction the window moves in perfect synchrony with their eye movements. The amount that this window of normal text extends to the right Normal reading relies on the reader making a series of saccadic and left of fixation is usually varied across trials in an experiment eye movements along each line of text, separated by periods of and is informative about the amount of text that must be shown brief fixational pauses during which the eyes are relatively normally at the reader’s point of fixation for reading performance stationary and visual information is acquired from the text (for to be normal. reviews, see [1,2]). However, the region of text from which this Studies using this paradigm have been highly informative about information primarily is acquired on each fixational pause (usually the perceptual span for English and other alphabetic systems that called the perceptual span, [2]) is limited. Estimates of the size of are read from left to right, and have shown that skilled readers of the perceptual span have been obtained using a gaze-contingent English obtain useful information from an asymmetric area that eye-tracking paradigm in which changes are made to text extends approximately 14–15 character spaces to the right of dependent on the location of the reader’s fixational pauses [3,4]. fixation but no more than about 3–4 character spaces to the left This typically involves displaying a region of text as normal at the [3–7] and typically no further than the beginning of the fixated reader’s point of fixation and obscuring text outside of this region word. These characteristics of the perceptual span for English (and (e.g., by replacing the original letters with xs). This region (or other languages that are read from left to right) seem to survive window) of normal text is moved in synchrony with the reader’s over various viewing conditions (e.g., viewing distance and size of eye movements, so that when the reader moves their eyes to fixate print [8,9]). Consequently, it is generally accepted that, when a new location, only text at this new location is shown normally reading from left to right, the perceptual span extends much and all other text is obscured. These changes are made sufficiently further to the right of fixation than to the left. rapidly that the reader has the phenomenological experience that PLOS ONE | www.plosone.org 1 February 2014 | Volume 9 | Issue 2 | e88358 The Central Perceptual Span in Urdu and English The nature of the perceptual span is nevertheless generally and have variable widths and shapes depending on their location, considered to reflect the written characteristics of the language and so may pose particular challenges to readers. Urdu is one of that is being read [10,11]. In particular, it is argued widely that the two national languages of Pakistan, alongside English, and is asymmetry in the perceptual span for alphabetic languages is widely used throughout Pakistan, Bangladesh, several regions of related to the overall direction of reading. Accordingly, the India, and amongst populations in Saudi Arabia, the UK, and perceptual span is asymmetrical to the right when reading English USA. It is not uncommon for well-educated individuals, partic- so that readers not only acquire information about the presently ularly those from Pakistan, to be bilingual in English and Urdu fixated word but also valuable information from parafoveal vision and to be able to read proficiently in both languages. An that might benefit the programming of saccadic eye movements assessment of asymmetry in the region of text required by these that move the reader’s point of fixation forward in text and benefit bilinguals when reading in Urdu and English is therefore well- the pre-processing of words to the right of the current point of suited to revealing more fully the influence of reading direction on fixation [12–17]. the perceptual span. Accordingly, and following the approach of However, while the perceptual span in English and other Pollatsek et al. [18], we investigated the perceptual span of languages that are read from left to right has been widely studied bilingual readers of Urdu and English using a version of the gaze- (for a recent review, see [2]), the nature of the perceptual span for contingent moving-window technique used in previous research to languages that are read from right to left has received much less control the amount of information available to the left and right of attention. Indeed, arguments for the role of reading direction in fixation during each fixational pause when English and Urdu is determining asymmetry in the perceptual span are usually based read. on findings from a single study by Pollatsek, Bolozky, Well, and However, rather than investigating the overall extent of the Rayner [18],which examined the perceptual span in Hebrew. In perceptual span, the focus of the present experiment was the this study, native Israeli readers who were bilingual in Hebrew and influence of information within an area extending 2.5u either side English read sentences in which a window of normal text extended of fixation. The reason for this approach is that the perceptual either 14 characters to the left of fixation and 4 characters to the span encompasses a range of different types of information (e.g., right, or 4 characters to the left of fixation and 14 characters to the inter-word spaces, word shape, letter identities; for a review, see right. The findings showed that reading performance for Hebrew [2]), broadly reflecting retinal eccentricity. Indeed, previous was superior when windows were asymmetric to the left whereas research using English suggests that letter identification during performance for English was superior when windows were reading extends to only 8 or 9 characters to the right of fixation asymmetric to the right. Thus, as Pollatsek et al. concluded, the (equal to approximately 2.5u of visual angle under normal reading overall direction of reading appears to modify the asymmetry of conditions) and just 4 characters (equal to approximately 1u) to the the perceptual span. However, this seminal study provided the sole left (e.g., [7,23]). But asymmetry in this area (which we call the evidence for more than 30 years that the perceptual span varies as central perceptual span) appears to be particularly influential for a function of the direction of reading in an alphabetic language. reading because it provides information which is required to Consequently, given the importance of this topic for understand- identify the fixated word and, crucially, important information ing the processes involved in reading, and for implementing these about the following word which aids the programming of saccadic processes in computational models of eye movement control (e.g., eye movements and parafoveal pre-processing.