Peripheral vision and pattern recognition: a review - strasburger - main

Peripheral_Vision.doc
High contrast character recognition and acuity in eccentric vision are crucially affected by the
deployment of spatial attention (Nakayama & Mackeben, 1989; Mackeben, 1999; Carrasco et
al., 2002; Talgar et al., 2004). Results depend on whether the subject knows where to expect
the stimulus, and whether and when there are spatial cues marking the target location. These
dependencies have been known since long (cf. Chapter 2); to eliminate that influence in acuity
measurement, researchers typically have chosen paradigms where the subject knows the
eccentric location. However, sustained attention has been shown to be anisotropic with a
dominance of the horizontal meridian in the macula (Mackeben, 1999). Performance at
disfavored locations was found to be limited by deploying attention, not by holding it there.
Attentional anisotropies thus need to be distinguished from anisotropies on the input side
(receptors, ganglion cells, LGN, V1). We return to the role of spatial attention in the context of
crowding (Chapter 5).
4.1.2 Character recognition at high contrast
Character recognition is a task with requirements very different from those of detection and
discrimination (cf. Chapter 8). The interest in these aspects arises in reading and dyslexia
research, which we will touch only briefly. Korte (1923) studied confusions and mis-readings of
letters in peripheral vision in the tradition of the Gestalt school. Since in his study letters were
presented in the context of syllables, we will come back to his account in the chapter on
crowding (cf. Chapter 5 and Appendix). Geiger and Lettvin (1987) introduced the form-resolving
visual field (FRF). It differs from acuity measurement in that (1) simple and more complex forms
are used (Zegarra-Moran & Geiger, 1993), (2) attention is divided between a foveal and the
perpheral form, and (3) size is kept constant; the dependent measure is percent correct.
Gervais, Harvey and Roberts (1984) also addressed human letter recognition psychophysically
outside the tradition of acuity research. The authors compared 26×26 confusion matrices for the
full 26-letter alphabet with predictions from a template model, a geometric feature model using
unstructured feature lists, and a model based on 2D Fourier descriptors weighted by the human
contrast sensitivity function (CSF). Letters were above the size threshold but were quite small
(0.1°) and were briefly presented so as to produce 50% correct performance. Results were
based on 3,900 trials. The highest correlation (0.70) between actual and predicted confusions
was attained by the model where letters were filtered by the human CSF, using both letter
amplitude and phase spectra, although the contribution of phase was moderate. The template
model ranked second, the geometric feature model third. This suggests that peripheral letter
recognition depends largely on contrast sensitivity. To our knowledge later studies of singleletter
confusions have not again looked at the full alphabet.
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