Perceptual span, visual span, and visual attention span: Three potential ways to quantify limits on visual processing during reading

ABSTRACT

Many lines of evidence have revealed limitations of the human visual system, most notably that only a portion of available information is processed in a single glance. A degree of conceptual confusion has emerged, however, regarding the underlying concepts or mechanisms explaining limited visual processing in reading; perceptual span, visual span, or visual attention span. While the original definitions of these three concepts are clear and well-differentiated, they are routinely used inconsistently in the literature. The primary goal of the present review is to re-specify these three concepts in terms of what they correspond to and how they are determined. Further, we investigate whether these three spans refer to vision-related measurements and/or are based on general cognitive abilities. This review should lead to a better understanding of the involvement of visual functions in reading performance.

KEYWORDS:

• Reading
• eye movements
• perceptual span
• visual span
• visual attention span

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Aline Frey http://orcid.org/0000-0002-0110-8633

Marie-Line Bosse http://orcid.org/0000-0002-9864-380X

Notes

1 Recent findings suggested that reading performance is actually quite tolerant of substantial restrictions to the visual input available for text brought into foveal vision (i.e., coarse, medium, or fine spatial frequency content; Jordan, McGowan, & Paterson, 2012).

2 We have also found the acceptation “visual apprehension span” (Starrfelt et al., 2009) defined as the maximum number of items that can be recognised in one view. As this term has been used in a limited context specific to literature focused on pathology (alexia), we have chosen to exclude it from this review.

3 Two additional techniques have previously been used to investigate PS: (1) dividing the number of words per line by the number of fixations per line; (2) using a tachistoscopic presentation of words and letters in eccentric vision. Both techniques presented significant limitations (Rayner, 1986).

4 More precisely, crowding was identified in the clinical vision literature in connection with amblyopia (Flom, Weymouth, & Kahneman, 1963; Levi & Klein, 1985) well before Bouma (1970), but the latter brought it to the attention of researchers interested in letter recognition and reading.

5 Alphabetic writing systems range from transparent to opaque, depending on their degree of consistency between grapheme to phoneme correspondences. A language in which each grapheme corresponds to a single phoneme is “transparent”. Conversely, when each grapheme can correspond to several phonemes, the language is considered “opaque”. However, the transparent/opaque dichotomy also reflects differences in the size of relevant orthographic units, and graphemes are typically shorter in more transparent languages (Awadh et al., 2016).

6 The visual span profiles tend to be slightly broader on the right than the left (Legge et al., 2001) when letters are presented within strings of other letters (crowded letters), but the recognition of isolated letters is the same in the left and the right visual field (Nazir, O’Regan, & Jacobs, 1991).