Foveal visual acuity is worse and shows stronger contour interaction effects for contrast-modulated than luminance-modulated Cs

Abstract

Contrast-modulated (CM) stimuli are processed by spatial mechanisms that operate at larger spatial scales than those processing luminance-modulated (LM) stimuli and may be more prone to deficits in developing, amblyopic, and aging visual systems. Understanding neural mechanisms of contour interaction or crowding will help in detecting disorders of spatial vision. In this study, contour interaction effects on visual acuity for LM and CM C and bar stimuli are assessed in normal foveal vision. In Experiment 1, visual acuity is measured for all-LM and all-CM stimuli, at ∼3.5× above their respective modulation thresholds. In Experiment 2, visual acuity is measured for Cs and bars of different type (LM C with CM bars and vice versa). Visual acuity is degraded for CM compared with LM Cs (0.46 ± 0.04 logMAR vs. 0.18 ± 0.04 logMAR). With nearby bars, CM acuity is degraded further (0.23 ± 0.01 logMAR or ∼2 lines on an acuity chart), significantly more than LM acuity (0.11 ± 0.01 logMAR, ∼1 line). Contour interaction for CM stimuli extends over greater distances (arcmin) than it does for LM stimuli, but extents are similar with respect to acuities (∼3.5× the C gap width). Contour interaction is evident when the Cs and bars are defined differently: it is stronger when an LM C is flanked by CM bars (0.17 ± 0.03 logMAR) than when a CM C is flanked by LM bars (0.08 ± 0.02 logMAR). Our results suggest that contour interaction for foveally viewed acuity stimuli involves feature integration, such that the outputs of receptive fields representing Cs and bars are combined. Contour interaction operates at LM and CM representational stages, it can occur across stage, and it is enhanced at the CM stage. Greater contour interaction for CM Cs and bars could hold value for visual acuity testing and earlier diagnosis of conditions for which crowding is important, such as in amblyopia.

Levelt’s laws do not predict perception when luminance- and contrast-modulated stimuli compete during binocular rivalry

“…This asymmetry is of opposite polarity and may be due to feed-forward pooling, different to what is considered here for different stimuli viewed under binocular rivalry conditions. Our asymmetry findings are more in line with those of Schofield and Kingdom (2014) 28 and Hairol, Formankiewicz and Waugh (2013) 29 . Schofield and Kingdom 28 used an orientation grouping paradigm with 0.4 deg, circular patches of luminance, colour or texture (binary noise on a mean background) to assess their comparative strengths.…”

“…Hairol et al . 29 found stronger contour interaction effects when CM bars surrounded an LM C during visual acuity assessment, than vice versa, suggesting stronger feedback effects may occur from a second CM stage. Finally, for binocularly viewed gratings (2 c/deg constructed from two-dimensional binary noise), spatial tilt and contrast after-effects for CM gratings, measured after viewing LM gratings and vice versa, were found to be similar rather than asymmetric 30 .…”

Visual acuity measured with luminance-modulated and contrast-modulated noise letter stimuli in young adults and adults above 50 years old

“…The stimuli were loaded on to the frame store memory of a VSG graphic card (Cambridge Research Systems) installed in the computer. Monitor calibration and gamma correction procedures were carried out every 3 to 6 months by using OptiCal photometer to avoid adjacent pixel nonlinearity ( Bertone et al , 2011 ; Hairol et al , 2013 ). In every session, the display monitor was turned on for at least 20 minutes to stabilise its luminance output before data collection commenced.…”

“…First-order or luminance-defined information is known to be processed by linear mechanisms through linear processing within the striate visual cortex (V1). Stimuli which portray variation in properties such as contrast, texture or orientation without any change in mean luminance are known as second-order stimuli ( Hairol et al , 2013 ; Sukumar & Waugh, 2007 ; Wong et al , 2001 ). Processing mechanisms of second-order stimuli are thought to be more complex, and occur in higher and more binocular areas of the visual cortex, than those of first-order stimuli ( e.g.…”

Perbandingan Zon Interaksi Ruang Dua Dimensi Subjek Normal dan Ambliopia Anisometropik

“…Apabila sesuatu rangsangan dikelilingi oleh objek yang lain, kebolehan seseorang untuk mengenal pasti objek tersebut merosot. Kesan ini berlaku untuk pelbagai jenis rangsangan seperti huruf, nombor dan gratings (Bouma 1970;Hairol et al 2015Hairol et al , 2013Strasburger et al 1991;Stuart & Burian 1962). Kesan kesesakan boleh bertambah dengan meningkatkan jumlah objek yang mengelilingi rangsangan tersebut (Felisberti et al 2005) dan kedudukan (esentrisiti) rangsangan yang menjauhi retina (Bouma 1970;Jacobs 1979) atau pun dengan mengurangkan jarak antara rangsangan dengan objek yang mengelilinginya (Flom et al 1963).…”