Early-visual factors in letter confusions

Abstract

For the purpose of quantifying models of letter recognition, similarities are often specified in terms of stimulus properties. In this paper, an approach is advocated based on similarities between internal letter representations or internal letter images, i.e. it is argued that optical and retinal factors play a more prominent role in letter confusions than is usually assumed. To illustrate this, letter images were calculated on the basis of earlier experimentally determined point spread functions (Blommaert et al., Spatial Vision 2, 99-115, 1987). Next, data on confusion matrices from Bouma (Vision Res. 11, 459-474, 1971) were taken to evaluate different measures which might be useful for quantifying similarities between internal letter representations. In the analysis of experimental data, Luce's (In: Handbook of Mathematical Psychology, 1963) choice model was used. It was found that if similarities were expressed in terms of differences between image contours, a fair first order approximation of Bouma's experimental results could be formulated (overall correlation coefficient of 0.95). Other measures like correlations between spatial frequency spectra of letter images were found to be less successful. The method used provides a means to relate quantitatively stimulus features and optical and early-visual factors to letter confusions.

Modeling acuity for optotypes varying in complexity

“…Our model also continues a tradition, that of template models (Blommaert, 1988;Gervais et al, 1984;Loomis, 1990;Watson & Fitzhugh, 1989). What we have shown here is that, based at least on the pattern of results in the confusion matrix, a template model performs better than the feature model of Liu et al (2009).…”

The dynamics of sensory buffers: Geometric, spatial, and experience-dependent shaping of iconic memory

“…On the other hand, it has been shown that in a cluttered field, the saliency of a stimulus is determined by a generalized distance, in feature space, to the field of distractors (Ashby & Lee, 1991;Duncan & Humphrey, 1989;Feldman, 2003;Feldman & Singh, 2005). This general finding of visual perception has been widely studied in the specific domain of letter perceptionVand from there on to word recognition (Nazir et al, 2004;Nazir, Jacobs, & O'Regan, 1998)Vdemonstrating that the matrix of confusion can be determined, to a large extent, by morphological proximity (either by space overlapping or by feature proximity) (Blommaert, 1988;Bouma, 1970Bouma, , 1971Chialvo, 1997;Gervais, Harvey, & Roberts, 1984;Townsend, 1971). In the more general case, however, other non-low-level sensory factors as well as acoustic confusions (Baddeley, 1966(Baddeley, , 1968) may contribute to letter confusion depending on the specifics of the task (Townsend, 1971).…”

Alphabetic letter identification: Effects of perceivability, similarity, and bias

“…For example, some researchers have used simple methods of letter congruency or overlap (e.g., Dunn-Rankin, Leton, & Shelton, 1968; Gibson, 1969) to measure letter similarity, whereas others have developed more elaborate techniques relying on Fourier decomposition (Blommaert, 1988; Coffin, 1978; Gervais, Harvey, & Roberts, 1984). These methods rarely make any commitments about biases or perceivability, and focus on producing objective measures of letter similarity.…”