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Previous studies of peripheral vision have shown that detection acuity is superior to resolution acuity for gratings over a range of contrasts, which is attributed to different limiting mechanisms (contrast insufficiency and neural undersampling) for the two tasks. To extend the analysis to letters in a way that avoided luminance cues, we used "vanishing optotype" characters, conveying second-order information, and constructed from tripole strokes having the same mean luminance as the surround. We measured the minimum letter size for detection and identification tasks for two different pairs of vanishing optotype characters (O vs. + and orthogonally oriented Landolt-C's) as a function of contrast in central and peripheral vision. Foveally there was no significant difference between detection acuity and resolution acuity for either pair of letters over a range of stimulus contrasts from 20% to 100%, indicating performance is contrast-limited for both tasks. The same result was obtained at 30° eccentricity in the peripheral field for the O vs. + letters, again indicating performance is contrast-limited for both tasks. However, resolution acuity for the Landolt-C letters was significantly worse than detection acuity in the periphery over the same range of contrasts, which suggests performance is limited by neural undersampling for these letters. All of our experimental results are explained by a model of neural sampling in which detection acuity is determined by the size of neural receptive fields relative to the dimensions of the tripole responsible for spatial contrast, whereas resolution acuity is determined by the spacing of receptive fields relative to the spacing between strokes responsible for letter form., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The spatial variation in central retinal function determined from mfERG was compared to co-localised measurements of cone density in two normal subjects. Individual cone cells in the parafoveal region of the retina were identified from 1 degrees x1 degrees images of the photoreceptor mosaic using a modified Heidelberg retina tomograph (HRT). The variation in cone density compared well with previous histology and retinal imaging studies and was strongly linearly correlated (r=0.98, p<0.001) with mfERG amplitude within the central retina. Retinal function determined from mfERG amplitude appears to directly reflect the density of the cone cells in this region., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Weber contrast, DeltaL/L, is a widely used contrast metric for aperiodic stimuli. Zele, Cao & Pokorny [Zele, A. J., Cao, D., & Pokorny, J. (2007). Threshold units: A correct metric for reaction time? Vision Research, 47, 608-611] found that neither Weber contrast nor its transform to detection-threshold units equates human reaction times in response to luminance increments and decrements under selective rod stimulation. Here we show that their rod reaction times are equated when plotted against the spatial luminance ratio between the stimulus and its background (L(max)/L(min), the larger and smaller of background and stimulus luminances). Similarly, reaction times to parafoveal S-cone selective increments and decrements from our previous studies [Murzac, A. (2004). A comparative study of the temporal characteristics of processing of S-cone incremental and decremental signals. PhD thesis, New Bulgarian University, Sofia, Murzac, A., & Vassilev, A. (2004). Reaction time to S-cone increments and decrements. In: 7th European conference on visual perception, Budapest, August 22-26. Perception, 33, 180 (Abstract).], are better described by the spatial luminance ratio than by Weber contrast. We assume that the type of stimulus detection by temporal (successive) luminance discrimination, by spatial (simultaneous) luminance discrimination or by both [Sperling, G., & Sondhi, M. M. (1968). Model for visual luminance discrimination and flicker detection. Journal of the Optical Society of America, 58, 1133-1145.] determines the appropriateness of one or other contrast metric for reaction time.

To determine the age-related change in the peripheral short-wavelength-sensitive (SWS) grating contrast sensitivity function (CSF), cut-off spatial frequency (acuity) and contrast sensitivity for both a detection and resolution task were measured at 8 degrees eccentricity under conditions of SWS-cone isolation for 51 subjects (19-72 years). The acuity for both the detection and resolution task declined with age, the detection acuity being significantly higher than the resolution acuity at all ages (p<.01). The CSF for both detection and resolution shifted towards lower spatial frequencies with increasing age. The contrast sensitivity for detection remained higher than that for resolution for all ages at the highest spatial frequencies. The age-related loss in the SWS resolution CSF at high spatial frequency probably reflects a loss occurring at the ganglion cells level.

We investigated relationships between retinal structure using optical coherence tomography (OCT) and retinal function using peripheral resolution acuity and multifocal electroretinograms (mfERG) in 56 subjects with a range of refractive errors (+0.50 to -15.00 D). Retinal thinning occurred in moderate and high myopia which appeared to be primarily due to reduced thickness of the middle to inner retina (MIR) (outer plexiform layer to the nerve fiber layer). MIR thickness was correlated with reduced spatial resolution and delayed mfERG timing in the peripheral retina. The findings suggest the structure and function of the post-receptor retina is susceptible to disruption in moderately and highly myopic eyes.

Short-wavelength-sensitive (SWS) resolution acuity has been reported to be limited by the density of the responding ganglion cells for people without appreciable age-related lenticular change. This study measured the robustness of SWS-cone acuity and contrast sensitivity (CS) to simulated lens yellowing and opacification. Resolution acuity at 8 deg eccentricity proved robust to significant amounts of yellowing and remained lower than detection acuity, indicating that the resolution continued to be limited by ganglion cell density. Both the detection and resolution CS functions were affected by simulated lens yellowing, except for resolution close to the CS cut-off. For simulated opacification, only dense opacity significantly affected performance. SWS resolution acuity and CS close to the resolution limit are resistant to moderate simulated age-related lens changes and continue to be mediated by the density of the responding ganglion cells, indicating important clinical potential to measure SWS neural losses of vision in older subjects.

We studied spatial summation for S-cone ON and OFF signals as a function of retinal eccentricity in human subjects. S-cone isolation was obtained by the two-colour threshold method of Stiles, modified by adding blue light to the yellow background. Test stimuli were blue light increments or decrements within a circular area of variable size. These were presented for 100 ms at 0 to 20 deg along the horizontal temporal retinal meridian. Ricco's area of complete spatial summation was measured from the threshold vs. area curves. This was nearly constant and approximately the same for both types of stimuli within the 0-5 deg range and increased beyond this range. The decremental area increased faster, suggesting that separate mechanisms, presumably ON and OFF, integrate S-cone increments and decrements. The results appear to provide new evidence for the existence of separate S-cone ON and OFF pathways. We compare the data with known morphology of primate retina and assume that, if S-cone decrements are detected via separate OFF cells, these should differ in density and dendritic field size from the S-cone ON cells, but only in the retinal periphery.

Previous studies have indicated that peripheral achromatic grating resolution is limited by the sampling density of the neural array (sampling limited), and largely unaffected by large amounts of optical defocus and significant changes in luminance. Under certain conditions, peripheral short-wavelength sensitive (SWS) grating acuity is also sampling limited. We wished to determine how the sampling-limited nature of SWS-driven grating resolution was affected by changing optical defocus and stimulus luminance. Using SWS-cone isolation techniques, detection and resolution acuity were measured for sinusoidal gratings under varying levels of stimulus mean luminance and optical defocus in the fovea and at 20 degrees eccentricity. From 1.4 down to 0.3 cd/m(2) peripheral detection acuity was superior to resolution acuity, accompanied by observations of aliasing: there was little change in resolution performance throughout this range. For defocus up to 3-4 dioptres, peripheral detection acuity was superior to resolution but fell steadily: resolution performance remained flat throughout the same range. Unlike achromatic acuity, foveal resolution performance displayed some robustness to defocus but to a lesser degree than the periphery. Peripheral SWS-driven resolution remains sampling limited for large changes in stimulus luminance and optical defocus, and should thus be useful as a clinical test of SWS-driven ganglion cell density., (Copyright 2002 Elsevier Science Ltd.)

Previous studies have indicated that peripheral resolution for achromatic gratings is sampling limited and directly related to the density of the underlying midget ganglion cell population. Previous studies by the authors have shown that peripheral resolution for blue-cone isolating gratings is also sampling limited, is robust to optical defocus and short-wavelength attenuation, and yields estimates of sampling density which correspond closely with the density of small bistratified ganglion cells. We measured peripheral resolution in a group of normal subjects ranging in age from 12 to 72 years, using both achromatic and blue-cone isolating gratings, to determine how performance (and hence ganglion cell density) changed with age for both systems. Resolution was higher for achromatic than blue-yellow gratings and performance was flat for both until the fifth decade. After this, performance declined for both at a rate of approximately 14%/decade with no significant difference between the two rates of decline. Individual measurements of lens density were not correlated with short-wavelength sensitive resolution performance in the older subjects, further indicating that the decline in resolution was not attributable to pre-retinal absorption., (Copyright 2002 Elsevier Science Ltd.)

Peripheral resolution acuity for achromatic gratings is known to be limited by the density of the underlying ganglion cell sampling array. After confirming isolation of the short-wavelength sensitive (SWS) system using chromatic adaptation methods, we wished to determine if resolution is limited by blue/yellow ganglion cell sampling (evidenced by a superiority of detection over resolution acuity and the perception of aliasing) and thus directly related to SWS-driven ganglion cell density. We measured detection and resolution acuity between 0 degrees and 35 degrees, using blue sinusoidal gratings superimposed on a yellow adapting background which ranged in intensity from 2.5 to 4.7logTrolands. At all locations, a break could be observed in the acuity vs. illumination curves followed by a plateau. Detection and resolution acuity were the same for low background intensities, but resolution acuity was lower than detection at higher intensities, accompanied by observations of chromatic aliasing. SWS resolution is sampling-limited across the retina and agrees well with predicted performance based on anatomical estimates of small bistratified ganglion cell density.

Peripheral monocular grating resolution has been shown to be limited by the sampling density of the underlying retinal ganglion cells. We wanted to determine if peripheral resolution is also sampling limited binocularly; and, if so, how great is any improvement in either detection or resolution when viewing binocularly? We measured detection and resolution acuity for sinusoidal gratings in foveal and peripheral vision both monocularly and binocularly. Detection and resolution acuity were very similar in foveal vision and displayed a binocular improvement of 5% over best monocular acuity. However, in peripheral vision, while detection acuity improved by 6% binocularly, resolution acuity improved by 16%, with a subsequently smaller aliasing zone. This improvement was greater than predicted by probability summation and implies that the two monocular ganglion cell sampling arrays combine at a higher level resulting in a higher binocular sampling density.

We measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30 degrees in the periphery to determine if peripheral resolution is sampling limited for this stimulus. In the fovea, where acuity is optically limited, detection and resolution were the same. At 30 degrees, however, detection was markedly better than resolution indicating that peripheral resolution is sampling limited for this stimulus. Detection acuity was higher when contrast was 90% rather than 40%, but resolution did not change with contrast. The vanishing optotype is a legitimate perimetric stimulus to measure retinal ganglion cell density provided the task is resolution and not detection.

We measured resolution acuity at 12 different retinal locations using sinusoidal gratings in a group of normals, ocular hypertensives and glaucoma patients. Resolution was measured using both stationary gratings, which selectively stimulate parvocellular ganglion cells (P cells), and gratings which phase reversed at 30 Hz, which selectively stimulate a higher proportion of magnocellular ganglion cells (M cells). With stationary gratings, peripheral resolution was found to be significantly reduced in glaucoma patients and, to a lesser extent, in ocular hypertensives. When the stimuli phase reversed at 30 Hz these differences between groups were larger. The ratio of resolution with and without phase reversal also showed a significant difference between the three groups. These results provide strong psychophysical evidence for a selective loss of M ganglion cell density over P ganglion cell density in glaucoma.