Recognition of band-pass filtered hand-written numerals in foveal and peripheral vision.
The purpose of the present study was to find out what differences between foveal and peripheral pattern recognition remain unexplained by the inhomogeneities of retinal sampling and the optics of the eye. We measured contrast thresholds for pattern recognition at different eccentricities. The effects of retinal sampling were homogenised by using M-scaling of the stimuli, and the effects of the optics of the eye were by-passed either by using strong external noise (signal-to-noise ratio is not affected by optical attenuation) or by computing retinal image contrast by means of the optical modulation transfer function. The stimuli were hand-written numerals filtered to two-octave bands of various centre object spatial frequencies (c/object). The results were described as contrast thresholds and recognition efficiency. At all eccentricities, lowest contrast thresholds and highest recognition efficiencies were found at medium object spatial frequencies. At high object spatial frequencies the peripheral retinal contrast thresholds and recognition efficiencies were nearly as good as at the fovea, but at low object spatial frequencies most of the data showed superiority of the fovea to the periphery. Therefore, at high object spatial frequencies peripheral recognition performance could be explained relatively well by the retinal sampling gradient, or equivalently by the cortical magnification factor, together with the effects of the optics of the eye. Some eccentricity dependent deterioration of recognition at low object spatial frequencies remained unexplained.
Näsänen
R
R
Department of Optometry and Vision Sciences, University of Wales, College of Cardiff, UK. nasanen@kruuna.helsinki.fi
O'Leary
C
C
D000465:Algorithms; D015350:Contrast Sensitivity; D005584:Fovea Centralis / Q000502:physiology; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D014794:Visual Fields