Visual Sensory Units and the Minimum Angle of Resolution

Weymouth, Frank W.

doi:10.1097/00006324-196309000-00006

Cited by 20 publications

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“…It is a reasonable assumption that the kind of acuity task that most closely parallels size-difference discrimination is the recognition of the orientation of the gap in a Landolt C. Using data from Shlaer (1937), the minimum angle of resolution (the reciprocal of visual acuity) for the gap in a Landolt C for central vision at a luminance equivalent to that used in the present experiments is found to be approximately 0.45 min, which corresponds closely to the mean of 0.48 min obtained in the present experiment from all Ss for all stimulus sizes (SD =0.036 min). For peripheral vision the data in Fig.4 that are taken from Westheimer (1967) show close agreement with the regression line from the present experiments; it should be noted that Westheimer's data were obtained from eccentricities less than IO deg; the acuity task in this case was again gap detection in a Landolt C. Weymouth (1958) has pointed out that functions that are linear with eccentricity are typically found for all types of acuity tests; he shows that intercept values go from 0.43 min for vernier acuity to 4.6 min for one S for the Landolt C (figures are again minimum angle of resolution). Slope values were found to vary from about 0.11 for motion acuity to 1.80 for the Landolt C. The intercept and slope values from the present experiments were 0.6 and 0.88, respectively, which fall within the error range of Weymouth's peripheral visual acuity data for 20 Ss on a Landolt C task.…”

Section: Size Discrimination In Peripheral Visionsupporting

confidence: 85%

Visual size difference discrimination: Effect of disc size and retinal locus

Matthews

1969

Perception & Psychophysics

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While there is abundant information on the performance of the human eye and visual system with respect to detecting the presence or absence of light, discriminating between intensities, area/intensity and time/intensity relationships, relatively little is known about visual performance in a size discrimination situation. The question that might be asked is how effective is the eye in discriminating size differences between two objects of similar shape with respect to such stimulus parameters as length, width, or, in the case of circles, diameter. Although such situations have received relatively little attention, it is possible to have a priori expectations of visual performance. There appear to be two immediate hypotheses worth considering: (1) Difference discrimination might be considered a function of the size or magnitude of the stimulus, i.e., it would follow an approximation to Weber's law or one of its later derivatives. (2) We may consider that such discrimination could be thought of as a form of acuity task, in which case the jnd would be constant irrespective of stimulus size.There is evidence to suggest that data can be found to support either of the above mentioned hypotheses depending upon the exact experimental conditions. Ono (1967) demonstrated that discrimination of the difference between the length of two lines gave a Weber-type relationship only when the two lines were spatially separated, thus forcing the S to make a temporal judgment by first looking at one line and then the other. If simultaneous comparison was permitted with the two lines close together, the jnd was found to be approximately constant within experimental conditions and between three-line lengths. Ono points out that Weber specified that the relationship between the jnd and the size of the stimulus was for nonsimultaneous comparison only. Thus, experimental situations that permit a nonsimultaneous comparison between stimuli, whether in time or by permitting eye movements so that S is able to look from one stimulus to the other, are likely to tell us more about short-term visual storage than immediate visual performance with respect to the size-difference discrimination of discs of light in a situation that permits simultaneous comparison only.In order to determine the validity of the analogy between visual size-difference discrimination and acuity, it is first necessary to establish whether the jnd between two discs of light is independent of the size of the discs. If the jnd is found to be constant, a second issue that should receive consideration is whether or not the jnd will increase as a function of the displacement of the discrimination task off the visual axis, since it is well established that visual acuity becomes progressively worse with increasing retinal eccentricity. The experiments described below are designed to give answers to these two specific issues. METHODThe description of the experimental method will be divided into two sections-first, dealing with size discrimination of discs in central vision as a fun...

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Section: Size Discrimination In Peripheral Visionsupporting

confidence: 85%

Visual size difference discrimination: Effect of disc size and retinal locus

Matthews

1969

Perception & Psychophysics

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“…When measured in terms of a minimum angle of resolution (MAR), rather than its reciprocal, acuity, a linear model matches both anatomical data (e.g. receptor density), as well as performance results on many low-level vision tasks [Weymouth 1958;Strasburger et al 2011]. Acuity models form the basis for the well-known theory of cortical magnification or M-scaling, which posits that enlarging a visual stimulus minimizes performance variation as it becomes increasingly peripheral.…”

Section: Human Visual Acuity In the Peripherymentioning

confidence: 91%

Foveated 3D graphics

et al. 2012

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We exploit the falloff of acuity in the visual periphery to accelerate graphics computation by a factor of 5-6 on a desktop HD display (1920×1080). Our method tracks the user's gaze point and renders three image layers around it at progressively higher angular size but lower sampling rate. The three layers are then magnified to display resolution and smoothly composited. We develop a general and efficient antialiasing algorithm easily retrofitted into existing graphics code to minimize "twinkling" artifacts in the lower-resolution layers. A standard psychophysical model for acuity falloff assumes that minimum detectable angular size increases linearly as a function of eccentricity. Given the slope characterizing this falloff, we automatically compute layer sizes and sampling rates. The result looks like a full-resolution image but reduces the number of pixels shaded by a factor of 10-15.We performed a user study to validate these results. It identifies two levels of foveation quality: a more conservative one in which users reported foveated rendering quality as equivalent to or better than non-foveated when directly shown both, and a more aggressive one in which users were unable to correctly label as increasing or decreasing a short quality progression relative to a high-quality foveated reference. Based on this user study, we obtain a slope value for the model of 1.32-1.65 arc minutes per degree of eccentricity. This allows us to predict two future advantages of foveated rendering: (1) bigger savings with larger, sharper displays than exist currently (e.g. 100 times speedup at a field of view of 70°and resolution matching foveal acuity), and (2) a roughly linear (rather than quadratic or worse) increase in rendering cost with increasing display field of view, for planar displays at a constant sharpness.

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“…We expect that, if third-order motion is perceived, it would be perceived at low temporal frequencies and in central vision, because Lu and Sperling (l995b) found that the third order (salience motion) mechanism has a much lower cutoff frequency (at 3 Hz) than does the motion energy system and it has coarser spatial resolution. Indeed, previous stimuli that were constructed to evade the first-order motion system (and that probably stimulated a combination of second-and third-order motion) have been found to require lower temporal and spatial frequencies than do first-order stimuli (Anstis, 1974;Millodot, Johnson, Lamont, & Leibowitz, 1975;Weymouth, 1958). So, in appropriately chosen viewing conditions (fovea, low temporal frequencies), it might be possible for the third-order system to dominate the motion extraction process.…”

Section: Apparatusmentioning

confidence: 99%

Second-order reversed phi

Lü

Sperling

1999

Perception & Psychophysics

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In a first-order reversed-phi motion stimulus (Anstis, 1970),the black-white contrast of successive frames is reversed, and the direction of apparent motion may, under some conditions, appear to be reversed. It is demonstrated here that, for many classes of stimuli, this reversal is a mathematical property of the stimuli themselves, and the real problem is in perceiving forward motion, which involves the second-or third-order motion systems or both. Three classes of novel second-order reversed-phi stimuli (contrast, spatial frequency, and flicker modulation) that are invisible to first-order motion analysis were constructed. In these stimuli, the salient stimulus features move in theforward (feature displacement) direction, but the second-order motion energy model predicts motion in the reoersed direction. In peripheral vision, for all stimulus types and all temporal frequencies, all the observers saw only the reversed-phi direction of motion. In central vision, the observers also perceived reversed motion at temporal frequencies above about 4 Hz, but they perceived movement in the forward direction at lower temporal frequencies. Since all of these stimuli are invisible to first-order motion, these results indicate that the second-order reversed-phi stimuli activate two subsequent competing motion mechanisms, both of which involve an initial stage oftexture grabbing (spatiotemporal filtering, followed by fullwave rectification). The second-order motion system then applies a Reichardt detector (or equivalently,motion energy analysis) directly to this signal and arrives at the reversed-phi direction. The thirdorder system marks the location of features that differ from the background (the figure) in a salience map and computes motion in the forward direction from the changes in the spatiotemporallocation of these marks. The second-order system's report of reversed movement dominates in peripheral vision and in central vision at higher temporal frequencies, because it has better spatial and temporal resolution than the third-order system, which has a cutoff frequency of 3-4 Hz (Lu & Sperling, 1995b).In central vision, below 3-4 Hz,the third-order system's report of resolvable forward movement of something salient (the figure) dominates the second-order system's report of texture contrast movement.There is mounting evidence that there are three parallel streams of visual motion computation-first-and second-order systems that are primarily monocular and a third-order binocular system (Lu & Sperling, 1995a, 1995b, 1996c. The first-order system extracts motion from drifting luminance modulations, and the secondorder system extracts motion from drifting texture contrast modulations. These primarily monocular systems use motion energy analyses (Adelson & Bergen, 1985) or, equivalently, elaborated Reichardt detectors (van Santen & Sperling, 1984. Both primarily monocular systems are fast (temporal cutoff frequency at 10-12 Hz) and approximately equally sensitive to a wide range of spatial -Accepted by previous editor, My...

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Visual Sensory Units and the Minimum Angle of Resolution

Cited by 20 publications

References 0 publications

Visual size difference discrimination: Effect of disc size and retinal locus

Visual size difference discrimination: Effect of disc size and retinal locus

Foveated 3D graphics

Second-order reversed phi

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