Temporal impulse and step responses of the human eye obtained psychophysically by means of a drift-correcting perturbation technique

Roufs, Jaj Jacques; Blommaert, Frans Frans

doi:10.1016/0042-6989(81)90225-x

Cited by 96 publications

(64 citation statements)

References 35 publications

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“…If the response of the teststimulus is kept sufficiently small with respect to that of the probe, one might say that the response of the teststimulus perturbates that of the probe. This is highly analogous to the situation in the temporal domain explained in detail in Roufs and Blommaert (1981). The spatial case is worked out in the Appendix.…”

Section: Theoretica! Formalismmentioning

confidence: 79%

The foveal point spread function as a determinant for detail vision

Blommaert¹,

Roufs²

1981

Vision Research

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Abstract-A point spread function, chosen to link contrast sensitivity and stimulus dimensions. can be obtained from measured thresholds by assuming small-signal-linearity and peak detection for the visual system. To that end a special case of summation of subthreshold signals (perturbation) is used. taking specific measures against the effect of sensitivity drift. The basic assumptions are tested simuitaneousl~-and confirmed. Other provisional assumptions tike radial symmetry and homogeneity were evaluated along a horizontal and a vertical meridian through the fovea. In the fovea no deviation from radial symmetry was found. The effect of inhomogeneity within the central fovea. seems to be too small to cause a significant change in the point spread function. The validity for predicting thresholds of stimuli exposing larger areas is tested. Annuli with varying radii show no significant aberration if probability summation is taken into account. Predicted disk thresholds, however, show a large discrepancy with experiment for radii larger than 2min arc. A possible extension of the model with multiple-detection units having tuned sizes is evaluated. INTRODUCfIONIn order to investigate characteristics of detail vision stimuli like Landolt C's, lines or gratings are generally used. Sometimes, radially symmetrical stimuli like disks and annuli are used to investigate lateral processing over short distances (Fiorentini and Maffei, 1970;Westheimer, 1967). The spatial processing of the visual system is rather inhomogeneously over the retina. This is demonstrated by data on visual acuity (Le Grand, 1967) and thresholds for disks (Kishto, 1970;Wilson, 1970). A review is made by van Doorn et al. (1972). The effect is also found with thresholds of lines (Hines, 1976;Wilson and Bergen, 1979; Limb and Rubinstein, 1977). Wilson and Bergen, ibid, stressing the importance of local measurement of the inhomogeneous system. used line sources instead of gratings as stimuli. However, line sources of the usual type still stimulate retinal parts with different properties. The use of point sources is an obvious further step, the more so, since it is not clear how much the discrepancy between measured thresholds and prediction based on a line spread function (e.g. Wilson and Bergen, 1979) is disguised by effects of the mentioned extension of the lines.A point spread or weighting function can be used to characterize the effect of a near-threshold-pointsource on the contrast sensitivity of neighbouring retinal points (e.g. van Meeteren, 1973;Kelly, 1975). However, the threshold changes which have to be measured to obtain such a function are very small. Consequently special measures have to be taken to eliminate the effects of unavoidable sensitivity drift in order to obtain the required precision.In this report the results of a technique to obtain a point spread function from threshold measurements is investigated and the predictive power is tested. This point spread function should represent the simple processing of the visual system, thus ...

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Section: Theoretica! Formalismmentioning

confidence: 79%

The foveal point spread function as a determinant for detail vision

Blommaert¹,

Roufs²

1981

Vision Research

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“…Consider first that two events that are physically transient will give rise to internal neural activity that is persistent. Indeed, psychophysical findings suggest that sensory inputs undergo a form of low-pass filtering as they are processed in the brain (de Lange, 1958;Roufs & Blommaert, 1981;Viemeister, 1979;Weisenberger, 1986). Taking the example of an audiovisual pair, it is likely that the internal response to a visual stimulus is prolonged relative to the internal response to an auditory stimulus (de Lange, 1958;Viemeister, 1979).…”

Section: Assumptions Underlying Analyses Of Sjsmentioning

confidence: 99%

Shifts of criteria or neural timing? The assumptions underlying timing perception studies

Yarrow

Jahn

Durant

et al. 2011

Consciousness and Cognition

123

211

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“…Their model is similar to Jaskowski's (1991) model in that it incorporates the same two discrimination evaluators (simultaneity and order), but with the added element of specifying the nature of the input to and output from the two evaluators. The input to the evaluators is modeled after the Roufs and Blommaert (1981) temporal impulse response function: 1 where the parameter t is time in milliseconds, b is a free parameter which controls the growth and decay rates of the curve, and k is a normalizing constant, (e/3)3, ensuring that the function's peak value is 1. The function is unimodal and positively skewed, taking on values from 0 to 1 for positive values of t. This function is used by Roufs and Blommaert (1981) to model transient responses of the visual system to fast luminance variations (flashes) occurring within a foveal field, and thus appears reasonable to use in the present context.…”

Section: Effects Of Amount Of Attention Allocated To the Location Of mentioning

confidence: 99%

Effects of amount of attention allocated to the location of visual stimulus pairs on perception of simultaneity

Carver

Brown

1997

Perception & Psychophysics

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This study examined whether a change in the amount of attention equallyallocated to two locations affects judgments of the simultaneity or successiveness of stimuli presented at those locations. Observers were cued to expect two brief flashes either to the left and right of fixation or above and below fixation. Stimulus onset asynchrony was randomly varied. On a small proportion of trials, the stimuli appeared at the unexpected locations. Observers were more likely to report the stimuli as simultaneous when they appeared in the unexpected locations. A model proposed to account for the data assumes that a brief stimulus event is represented by a probability distribution reflecting the uncertainty in determining the time ofthe event's occurrence, and two events are judged to be simultaneous if they are perceived to fall within some critical temporal interval, C, which is a function of the amount of attention allocated to the task It has long been recognized that the perceived order of a pair of closely timed stimuli does not always correspond to the actual order of their occurrence (see James, 1890). The idea that some stimuli could receive perceptual or attentional priority for further processing led to the notion of"prior entry," which was the notion that there were factors that could alter the time it took for a stimulus to reach awareness (see Boring, 1950). The physical intensity of a stimulus is one strong determinant of prior entry (e.g., Roufs, 1963). More recently, Sekuler, Tynan, and Levinson (1973) uncovered what seemed to be an inherent bias in the visual modality toward more accurate recognition ofthe temporal order ofleft-first-right-second stimuli over right-first-left-second stimuli. The observed bias could be due to a left-right scanning mechanism such as is assumed to occur in reading, which would make the bias an attentional effect. Using a location-cuing manipulation, Stelmach and Herdman (1991) demonstrated that the direction ofattention could bias the perception of the temporal order of two visual stimuli: stimuli appearing in the attended location were more likely to be perceived first than were stimuli appearing in the unattended location (see also Hikosaka, Miyauchi, & Shimojo, 1993).While it is clear that an attentional bias can affect judgments of temporal order and simultaneity, a related question that, to our knowledge, has not yet been addressed is whether the overall level ofattention directed toward both stimuli in a temporal order task has any effect on judgments of temporal order or simultaneity. Does attention increase the precision ofjudgments of the relative time ofThe authors wish to thank Arthur Kramer and two anonymous reviewers for their helpful comments on earlier versions of this paper. Correspondence can be addressed to either R. A. Carver or V Brown, Department of Psychology, University of Texas, Arlington, TX 76019-0528 (e-mail: rcarver@uta.edu or brown@uta.edu).occurrence of two stimulus events? Conversely, to what extent are such judgments harmed by a decrease in the...

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Temporal impulse and step responses of the human eye obtained psychophysically by means of a drift-correcting perturbation technique

Cited by 96 publications

References 35 publications

The foveal point spread function as a determinant for detail vision

The foveal point spread function as a determinant for detail vision

Shifts of criteria or neural timing? The assumptions underlying timing perception studies

Effects of amount of attention allocated to the location of visual stimulus pairs on perception of simultaneity

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