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Showing papers in "Spatial Vision in 1997"


Journal Article•DOI•
TL;DR: The Psychophysics Toolbox is a software package that supports visual psychophysics and its routines provide an interface between a high-level interpreted language and the video display hardware.
Abstract: The Psychophysics Toolbox is a software package that supports visual psychophysics. Its routines provide an interface between a high-level interpreted language (MATLAB on the Macintosh) and the video display hardware. A set of example programs is included with the Toolbox distribution.

16,594 citations


Journal Article•DOI•
Denis G. Pelli1•
TL;DR: The VideoToolbox is a free collection of two hundred C subroutines for Macintosh computers that calibrates and controls the computer-display interface to create accurately specified visual stimuli.
Abstract: The VideoToolbox is a free collection of two hundred C subroutines for Macintosh computers that calibrates and controls the computer-display interface to create accurately specified visual stimuli. High-level platform-independent languages like MATLAB are best for creating the numbers that describe the desired images. Low-level, computer-specific VideoToolbox routines control the hardware that transforms those numbers into a movie. Transcending the particular computer and language, we discuss the nature of the computer-display interface, and how to calibrate and control it.

10,084 citations


Journal Article•DOI•
Denis G. Pelli1•
TL;DR: Two tests are recommended for assessing a CRT's deviation from the pixel-independence model, because most monitors have inadequate video bandwidth, DC restoration, and high-voltage regulation to live up to this ideal model.
Abstract: The standard working assumption of careful CRT imaging is that each pixel is imaged independently, through a point nonlinearity (the monitor's gamma function, relating screen luminance to input voltage), and then blurred by the point-spread function of the beam spot on the phosphor. Unfortunately most monitors have inadequate video bandwidth, DC restoration, and high-voltage regulation to live up to this ideal model. Two tests are recommended for assessing a CRT's deviation from the pixel-independence model.

371 citations


Journal Article•DOI•
TL;DR: A look-up table algorithm is described for enhancing the luminance resolution at the expense of the colour resolution in digital displays of colour images and can reduce the minimum luminance step in the mid-luminance range from 1.5% to > 0.2% with no additional hardware.
Abstract: A look-up table algorithm is described for enhancing the luminance resolution at the expense of the colour resolution in digital displays of colour images. For colour displays with a look-up table resolution of 8 bits/gun, the algorithm provides a luminance resolution of 11-12 bits without loss of spatial or temporal resolution. This improvement can reduce the minimum luminance step in the mid-luminance range from 1.5% to > 0.2% with no additional hardware.

104 citations


Journal Article•DOI•
TL;DR: PsyScope is a system for building behavioral experiments on the Apple Macintosh computer using a graphic user interface that requires no computer programming.
Abstract: PsyScope is a system for building behavioral experiments on the Apple Macintosh computer using a graphic user interface that requires no computer programming. The program supports a wide variety of experimental designs, multimedia formats, and stimulus control. A freeware version is available at the author's web site.

103 citations


Journal Article•DOI•
TL;DR: Raster-based cathode-ray tubes (CRTs) are increasingly used for stimulus presentation, but their design based on consumer electronics can limit their value in vision research.
Abstract: Raster-based cathode-ray tubes (CRTs) are increasingly used for stimulus presentation. While very flexible, their design based on consumer electronics can limit their value in vision research. Here their limitations of resolution in time, space, intensity and wavelength are systematically compiled. Often, ingenious ideas can circumvent such limitations for specific experiments. Some ad-hoc solutions, as well as the more general techniques of dithering and anti-aliasing, are presented.

100 citations


Journal Article•DOI•
TL;DR: It is shown that eye-movement traces made by different observers in response to the same image have few common temporal sequences involving the same fixation locations, even for sequences of only two fixations, and that the temporal sequence in which fixations are made is not a significant factor in the analysis of the eye- Movement data.
Abstract: Eye movements made by eighteen observers in response to brief (3 s) presentations of eleven different images, each in three forms (unfiltered, high-pass filtered and low-pass filtered), have been analysed in order to identify both repeated sequences of fixations and image locations which attract re-fixations. It is shown that eye-movement traces made by different observers in response to the same image have few common temporal sequences involving the same fixation locations, even for sequences of only two fixations. There is a greater incidence of such sequences in eye-movement traces made by the same observer in response to two presentations of the same image, but average numbers are still low. Conserved sequences involving more than two identical locations occur at a much lower frequency, and the incidence of repeated sequences is not increased if consideration is restricted to regions of the image which attract large numbers of fixations. It is concluded that the temporal sequence in which fixations are made is not a significant factor in the analysis of the eye-movement data considered in this report. Calculations based on a least squares index of similarity are consistent with this conclusion. The analysis shows a relatively high incidence of re-fixation on certain locations in the images and there is evidence that such re-fixations are a significant factor in the high similarity between fixation locations established by different observers when viewing the same image.

99 citations


Journal Article•DOI•
TL;DR: A suite of computer programs is described for visual field-assessment and training of residual vision in neuropsychological rehabilitation.
Abstract: A suite of computer programs is described for visual field-assessment and training of residual vision in neuropsychological rehabilitation

70 citations


Journal Article•DOI•
TL;DR: A set of C and C+2 routines are described that allow the efficient estimation of sensory thresholds in psychophysical experiments using a maximum-likelihood staircase procedure.
Abstract: A set of C and C+2 routines are described that allow the efficient estimation of sensory thresholds in psychophysical experiments using a maximum-likelihood staircase procedure. They have been used effectively in visual, auditory, gustatory, and olfactory psychophysics.

65 citations


Journal Article•
TL;DR: A computer program is described that uses a move reliable bootstrap approach to obtaining estimates of the standard deviation and confidence limits of a threshold and of the slope and spread of the psychometric function for any criterion level of performance.
Abstract: Estimates of the accuracy of a threshold obtained from a psychometric function are often based on asymptotic theory. When the number of trails is small, however, these estimates may be untrustworthy. A computer program is described that uses a move reliable bootstrap approach to obtaining estimates of the standard deviation and confidence limits of a threshold and of the slope and spread of the psychometric function for any criterion level of performance.

56 citations


Journal Article•DOI•
TL;DR: Software for measurement of psychophysical thresholds with 2D moving and coloured images is described, which is menu-driven and has contrast resolution to 0.2% without hardware modifications.
Abstract: Software for measurement of psychophysical thresholds with 2D moving and coloured images is described. It is menu-driven and has contrast resolution to 0.2% without hardware modifications. A calibrator to provide the full calibration of the Macintosh monitor required by the software is also described.

Journal Article•
TL;DR: YAAP is an implementation of an adaptive psychophysical method, based on Bayesian statistics, for estimating the threshold of a psychometric function on the basis of Bayesian probability intervals.
Abstract: YAAP is an implementation of an adaptive psychophysical method, based on Bayesian statistics, for estimating the threshold of a psychometric function. On the basis of Bayesian probability intervals, a dynamic termination criterion allows for threshold estimation within pre-specified confidence limits.

Journal Article•DOI•
TL;DR: Three experiments investigating the claim that the visual system utilizes a primitive indexing mechanism (sometimes called FINSTS) to make non-contiguous features directly accessible for further visual processing support the basic claim of the indexing theory: the Claim that multiple visual indexes are used in selecting objects for visual processing.
Abstract: This paper presents three experiments investigating the claim that the visual system utilizes a primitive indexing mechanism (sometimes called FINSTS; Pylyshyn, 1989) to make non-contiguous features directly accessible for further visual processing. This claim is investigated using a variant of the conjunction search task in which subjects search among a subset of the items in a conjunction search display for targets defined by a conjunction of colour and orientation. The members of the subset were identified by virtue of the late onset of the objects' place-holders. The cued subset was manipulated to include either homogenous distractors or mixed distractors. Observers were able to select a subset of three items from among fifteen for further processing (Experiment 1); furthermore, a reaction time advantage for homogenous subsets over mixed subsets was observed, indicating that more than one of the subset is selected for further specialized processing. The homogeneous subset advantage held for subsets of two to five items (Experiment 2), and the time required to process the cued subset did not increase with increased dispersion of the items (Experiment 3). These results support the basic claim of the indexing theory: the claim that multiple visual indexes are used in selecting objects for visual processing.

Journal Article•DOI•
TL;DR: The VisionWorks system is described-an integrated hardware and software experiment work-station for visual psychophysics and neurophysiology that is continually being updated to meet the ever-changing needs of vision researchers.
Abstract: We describe the VisionWorks system-an integrated hardware and software experiment work-station for visual psychophysics and neurophysiology. While the system already incorporates a large variety of stimuli and psychophysical methods, it is continually being updated to meet the ever-changing needs of vision researchers.

Journal Article•DOI•
TL;DR: Psychophysica is a set of software tools for psychophysical research that provides functions for calibrated visual displays, for fitting and plotting of psychometric functions, and for the QUEST adaptive staircase procedure.
Abstract: Psychophysica is a set of software tools for psychophysical research Functions are provided for calibrated visual displays, for fitting and plotting of psychometric functions, and for the QUEST adaptive staircase procedure The functions are written in the Mathematica programming language

Journal Article•DOI•
TL;DR: Rapid acquisition of a semi-objective and reliable acuity estimate makes the 'Freiburg Visual Acuity Test' useful for subject screening in vision research, as well as for routine assessments in the ophthalmic practice.
Abstract: Anti-aliasing is a technique for improving spatial resolution at the cost of luminance resolution. Dithering is a technique for improving luminance resolution at the cost of spatial resolution. These techniques are applied to the testing of visual function in the 'Freiburg Visual Acuity Test': by employing anti-aliasing, spatial resolution was improved. Thus, even the shape of small Landolt-Cs with oblique gaps is adequate, and visual acuities from 5/80 (0.06) up to 5/1.4 (3.6) can be tested at a distance of 5 m. By employing dithering, subthreshold contrast stimuli can be generated on a conventional display having standard 8-bit video resolution. Rapid acquisition of a semi-objective and reliable acuity estimate makes the 'Freiburg Visual Acuity Test' useful for subject screening in vision research, as well as for routine assessments in the ophthalmic practice.

Journal Article•DOI•
TL;DR: It is shown here how chromatic stimuli, namely (1) red/green and (2) purple/green (tritanopic) gratings, can be optimized for selective stimulation of the colour system.
Abstract: Anatomically distinct parvo and magno visual pathways show considerable functional overlap. However, specific stimulation of the most sensitive colour-opponent parvo-neurones is still possible, provided that colour stimuli are verified for selectivity. The authors have shown that gratings of low contrast, low spatial frequency and of restricted spatial content (6 or less spatial cycles) are optimal stimuli for distinguishing between colour-related (tritan and red/green) from achromatic or partly chromatic responses. This is particularly important when recording global responses, such as visual evoked potentials, VEPs. The crucial point is that at low presentation rates (< 2 Hz), colour-related onset VEPs are maximally different from contrast reversal VEPs, thereby reflecting the activity of sustained-type parvo mechanisms. Achromatic onset, offset and reversal VEPs are similar, reflecting mediation by transient-type magno mechanisms. A stringent test of colour-response specificity is to check whether the chromatic reversal VEP has a low-pass temporal tuning curve, since it becomes band-pass when substantial achromatic intrusions are present. Specification of chromatic isoluminant stimuli, e.g. along cardinal axes, does not guarantee their colour-selectivity, if chromatic aberration and variable macular pigmentation changes the chromatic content of the retinal image. It is shown here how chromatic stimuli, namely (1) red/green and (2) purple/green (tritanopic) gratings, can be optimized for selective stimulation of the colour system.

Journal Article•
Macmillan Na1, Creelman Cd•
TL;DR: The program d'plus calculates accuracy (sensitivity) and response-bias parameters using Signal Detection Theory, and 'nonparametric' models for forced-choice, same different, ABX, and oddity experimental paradigms.
Abstract: The program d'plus calculates accuracy (sensitivity) and response-bias parameters using Signal Detection Theory. Choice Theory, and 'nonparametric' models. is is appropriate for data from one-interval, two- and three-interval forced-choice, same different, ABX, and oddity experimental paradigms.

Journal Article•DOI•
TL;DR: Together, the fiberscope and CRT conveniently display accurately controlled high- and low-contrast wide-field images to an observer in an fMRI scanner.
Abstract: A binocular pair of fiberscopes relays high-resolution images of CRT displays from an adjacent room to an observer lying in a scanner in functional Magnetic Resonance Imaging (fMRI) studies of visual function. We review the problems that must be overcome by any visual display for use in fMRI, present the specific solution we developed, and discuss its merits. Together, the fiberscope and CRT conveniently display accurately controlled high- and low-contrast wide-field images to an observer in an fMRI scanner.

Journal Article•DOI•
TL;DR: Physical measurements of P31 persistence occurring with grating patterns of a mean luminance of 20 cd m-2 were obtained by using an extremely linear photometer with high temporal resolution and demonstrate a fast decay of residual grating contrast to 1.4% of its original value within 50 ms after pattern offset.
Abstract: P31 phosphor screens are frequently used for short-term presentation of dot and grating pat- terns, but experimental data obtained with this technique have been criticized because of possible parasitic effects of phosphor persistence on subjects' visual performance. Recently, this issue provoked a contro- versial discussion in Vision Research (Groner et al., 1993; Westheimer, 1993, 1994; Irwin, 1994; Di Lollo et al., 1994) which was concerned with persistence effects of P31 screens for dot patterns. Supplementing this discussion, the present work deals with the effects of different types of patterns (dot pattern vs. grat- ings) and background mean-luminance levels (scotopic vs. phototopic) on phosphor persistence. Physical measurements of P31 persistence occurring with grating patterns of a mean luminance of 20 cd m-2 (i.e. photopic range) were obtained by using an extremely linear photometer with high temporal resolution. Under this photopic condition, the measurements demonstrate a fast decay of residual grating contrast to 1.4% of its original value within 50 ms after pattern offset. This phosphor behavior must be considered when designing an experiment with a P31 screen though it certainly embodies no problems in many applications.

Journal Article•DOI•
TL;DR: An alternative calibration method is described that uses an iterative measurement procedure to obtain screen specifications that are accurate regardless of the display complexity, so that researchers can be confident that the required colours are actually displayed on the screen.
Abstract: This paper focuses on two issues that are important to those who use colour monitors for research in vision. One is concerned with the measurement and calibration of colour screens. To this end the luminance and chromaticity readings of a tri-filter colorimeter and a spectroradiometer are compared (both commonly used to calibrate screens). The second is concerned with screen interactions, whereby colours can be distorted from their expected or calculated values by the colours displayed in neighbouring areas. This issue is crucial for those who use measurements of the light emitted from the red, green and blue phosphors of a monitor in isolation to specify other colours on screen, particularly in the research areas of colour contrast and colour constancy, since the specified colours may not actually be displayed. Finally, an alternative calibration method is described that uses an iterative measurement procedure to obtain screen specifications that are accurate regardless of the display complexity, so that researchers can be confident that the required colours are actually displayed on the screen.

Journal Article•DOI•
TL;DR: Reading from a video display terminal (VDT) was tested at screen refresh rates of 500 Hz and 60 Hz and subjects were unaware of refresh conditions, differences in their reading rates, and types of eye movements they generated.
Abstract: Reading from a video display terminal (VDT) was tested at screen refresh rates of 500 Hz and 60 Hz. Reading was initially 8 words/min (3.05%) faster at 500 Hz. A hypothesis that reading rate on VDTs is limited by stimulus availability accounts for the difference. When the eye reaches a new fixation position, it 'parks' until a sample of text appears at the fovea. Then processing resumes in the normal way. This idea, combined with the 500-Hz reading data, can predict reading rate at any refresh rate, and is quantitatively confirmed by the reading rate at 60 Hz. The difference in reading rates disappeared for the second half of the text, as a result of differences between frequencies of eye movements in the two refresh conditions. From the first half to the second, subjects at 60 Hz made more large forward saccades and fewer small reverse saccades. Both changes make sampling of the text more sparse, compensating for the dead time between samples. Subjects were unaware of refresh conditions, differences in their reading rates, and types of eye movements they generated. Reading from a continuously illuminated active-matrix display is slightly faster than from a comparable VDT.

Journal Article•DOI•
TL;DR: In this article, a new moving-window technique is presented, which uses a purpose-designed video switcher and three synchronized video boards to select between the video signals of the first and second video boards on a pixel-by-pixel basis, controlled by the key signal generated by the third video board.
Abstract: Moving-mask and moving-window paradigms are used to study the spatial and temporal aspects of visual information processing. Due to technical limitations, these paradigms have frequently been applied to reading, but only rarely to scene perception. Existing moving-mask or moving-window techniques for graphical stimuli usually blank the display inside or outside a square window, respectively. A new moving-window technique is presented here that uses a purpose-designed video switcher and three synchronized video boards. The first video board contains the stimulus presented inside the window. The second video board contains the stimulus to be presented outside the window. The third video board contains a black-and-white image of the window that is used as a key signal for the video switcher. The video switcher selects between the video signals of the first and the second video board on a pixel-by-pixel basis, controlled by the key signal generated by the third video board. By panning the image of the third video board, the window can be moved very rapidly. Here we use oval windows, centered on the fixation spot as measured by an eye-tracker. The normal stimulus is visible inside the window, whereas manipulated information is presented outside the window, or vice versa.

Journal Article•DOI•
TL;DR: The period for which phosphor decay remains visible after stimulus offset was assessed for four phosphors commonly used in psychophysical experiments and it was concluded that P15 is the phosphor of choice for visual experiments.
Abstract: The period for which phosphor decay remains visible after stimulus offset was assessed for four phosphors commonly used in psychophysical experiments: P4, P15, P31, and P46. Stimuli were displayed behind closed shutters which opened at various intervals after stimulus offset. Thus, the observers' responses were based solely on the visibility of phosphor persistence. We varied viewing conditions (dark-adapted vs. veiling light), type of task (detection vs. identification), and intensity of the stimuli. No detectable persistence was ever produced by the P15 phosphor. In contrast, the P31 phosphor remained visible for several hundred ms. even with a veiling light. The P4 and P46 phosphors produced persistence of intermediate durations. It is concluded that P15 is the phosphor of choice for visual experiments.


Journal Article•DOI•
TL;DR: Several approaches and a tested solution designed to run on any PC or compatible under Windows 3.1/95, regardless of the video card used are described, which creates new possibilities for low-cost, implementation of visual experiments for laboratory and classroom use.
Abstract: As the use of computers for delivering stimuli in vision research has become ubiquitous, there is an obvious need for accurate timing of display monitors without the use of expensive hardware extensions. If a user should decide to program an application in the increasingly common 'Windows' operating system for IBM PCs and compatibles, a software solution for this problem is not obvious any more. The goal is to achieve display durations down to one single video frame. This article describes several approaches and a tested solution designed to run on any PC or compatible under Windows 3.1/95, regardless of the video card used. This creates new possibilities for low-cost implementation of visual experiments for laboratory and classroom use.

Journal Article•DOI•
TL;DR: R_Contrast is a program for the rapid assessment of recognition contrast thresholds on the PC and aims to provide real-time information on the strength of the contrast levels observed in a discrete-time environment.
Abstract: R_Contrast is a program for the rapid assessment of recognition contrast thresholds on the PC.

Journal Article•DOI•
Hans Irtel1•
TL;DR: PXL is a library for the procedural control of experiments which also provides many high-level utility functions and a collection of standard experiments with source codes.
Abstract: PXL is a library for the procedural control of experiments which also provides many high-level utility functions. A collection of standard experiments with source codes is available.

Journal Article•DOI•
TL;DR: Technical measurements of the Sony Multiscan 17se were made and are reported in the belief that they would be useful to visual scientists who consider employing this device as a display unit.
Abstract: Technical measurements of the Sony Multiscan 17se were made and are reported in the belief that they would be useful to visual scientists who consider employing this device as a display unit. Luminance, spatial uniformity, luminance additivity between the output of the guns, CIE1931 chromaticity coordinates, and gamma correction parameters were measured. The characteristics of individual monitors will probably be different from the one studied here but it is believed that the results obtained serve as a fair indication of what might be expected from this device.

Journal Article•DOI•
TL;DR: This article expands and quantifies one of the classic reports of modern visual perception research--Harmon and Julesz' (1973) demonstration of an enhancement in recognition performance when area averaging (blocking) and spatial frequency filtering are sequentially applied and confirmed the presence of the phenomenon for stimuli subtending approximately six deg of visual angle vertically.
Abstract: This article expands and quantifies one of the classic reports of modem visual perception research-Harmon and Julesz' (1973) demonstration of an enhancement in recognition performance when area averaging (blocking) and spatial frequency filtering are sequentially applied. Our goals were twofold: first, to determine if the existence of the phenomena could be confirmed and replicated in a parametric study; second, to determine if the new results supported the critical band masking theory originally proposed by Harmon and Julesz. We confirmed the presence of the phenomenon for stimuli subtending approximately six deg of visual angle vertically, but observed a surprisingly different pattern of results for smaller stimuli subtending approximately one deg. These and other recent findings from other laboratories raise questions about their masking theory as a complete explanation of the phenomena.