A vision research apparatus for broad luminance range displays

Lightness, the perceived gray shade of a surface, and the perception of self-luminous surfaces—that is, surfaces that appear to glow—have most often been studied with paper displays and computer-generated stimuli presented on CRT monitors. Although both methods are often effective, experiments that require a wide range of luminance values in the same display are often difficult to conduct with paper and computer displays alone. Also, color mode appearance is often an issue when surface color perception is the topic of research; CRT monitors are essentially light sources themselves and often appear in the luminous mode of color appearance. Here, we describe an apparatus in which the target is an undetected aperture whose luminance is adjustable. Whereas a typical CRT monitor offers a luminance range of about 100:1, much broader luminance ranges are possible with the described apparatus. Unlike a CRT monitor, the stimulus background will always appear in the surface mode of color perception, and the target(s) can appear as either surface colors or luminous colors. Apparatus modifications are possible, including the addition of a stereoscope or an embedded CRT for creating an adjustable region that is computer controlled.     

The noisy-bit method for digital displays: Converting a 256 luminance resolution into a continuous resolution

Visual psychophysics often manipulates the contrast of the image on a digital display screen. Therefore, the limitation of the number of different luminance intensities displayable for most computers (typically, 256) is frequently an issue. To avoid this problem, experimenters generally need to purchase special hardware (graphic cards) and/or develop specific computer programs. Here, we describe an easy-to-implement method, consisting of adding noise to the displayed stimulus, that we call the noisy-bit method. This random dithering method, generalized to 256 luminance intensities, is equivalent to displaying continuous luminance intensities plus a certain amount of noise. Psychophysical testing using a standard spatiotemporal resolution (60 Hz and 1,024 x 768 pixels) demonstrated that the noise introduced by the noisy-bit method has no significant impact on contrast threshold and is not visible. We conclude that the noisy-bit method, combined with the standard 256 luminance levels, is perceptually equivalent to an analog display with a continuous luminance intensity resolution when the spatiotemporal resolution is high enough that the noise becomes negligible (which is easily attainable with the typical spatiotemporal resolutions of present-day computers).     

On central vision activity and peripheral sensitivity: A method with potentialities for research on a range of problems in visual perception

Peripheral sensitivity of the human eye, P_s, and the processing capacity of the central retina, V_c, are assumed to be inversely related. On this basis, a method was designed, whereby P_s as a function of V_c can be determined and a family of P_s maps for the whole surface of the periphery can be obtained. This can be done by means of an experimental system consisting of a computer-based visual field, a hemisphere, on which tracking patterns with varying degrees of difficulty are displayed centrally (V_c) and multivariate signals (to be detected) are simultaneously presented on the periphery (as indexes of P_s). Since the apparatus is capable of producing and controlling a great number of variables, it can, with slight or no modifications, be used to study a wide range of problems in the field of visual perception and attention.     

Millisecond-accurate synchronization of visual stimulus displays for cognitive research

A widely adopted approach in cognitive psychology research is to analyze changes in the response time to a stimulus onset in order to infer information about the cognitive functioning of a subject being tested. But current techniques have inherent variations in the timing between stimulus activation and stimulus display of up to tens of milliseconds, thereby introducing significant errors when response time or the latency of neural responses is measured. This article presents a novel yet easy-to-implement solution for improving resolution in the synchronizing of stimulus activation and stimulus display. Unlike traditional methods in which the stimulus onset is set as the time at which the routine for displaying the stimulus is called, this approach uses DirectX to monitor the scan line of CRTs and sets the stimulus onset to the time at which the scan line arrives at the position where the stimulus is to be drawn. This approach removes the uncertainty involved in having a time delay between the activation of the display routine and the actual time at which the display occurs, improving the accuracy of response time and latency period measurements to within 200 μsec. With a specially developed driver, this solution can generate a trigger signal synchronized precisely with the stimulus onset in all popular Windows systems (including Windows 2000/XP).     

Computation of cone contrasts for color vision research

Cone-contrast coordinates have proved useful for representing transient test stimuli used in color vision experiments. These representations automatically take into account the spectral absorption of cones and any Weberian adaptation to steady fields of light. Under these conditions, they also can be interpreted as being an approximation to the incremental cone response. A detailed methodology is presented for making appropriate measurements and calculations of cons contrasts for any light source, especially color monitors.     

A microphotometer for measuring luminance distributions on a CRT

A relatively inexpensive microphotometer is described. The output voltage of the microphotometer is a linear function of luminance, and the sensitivity of the photometer is sufficient for the measurement spot size of .2 mm without special averaging devices. The rise and decay time of the photometer response is less than 100 microsec, and the spectral sensitivity of the photometer can be corrected to approximate that of the human photopic eye.     

Dynamic stereo displays for research on the recovery of three-dimensional structure

Research issues that can be addressed by combining stereoscopic and kinetic depth displays include cue conflict and recalibration, mutual constraints, specialization of cues, and differential effects of disparity and kinetic depth on other perceptions, such as size constancy. Methods of producing dynamic stereoscopic displays are reviewed, especially displays combining stereoscopic with orthographic projections of rotation in depth. A sample personal computer program in Pas-cal is provided.     

An apparatus for use in 2 by 2 game research

This article describes a solid state apparatus for use in 2 by 2 game research. There are two individual player’s boards and a control panel for E. Following E’s signal, each player chooses one of two responses. Their choices are immediately registered on E’s panel, but appear on each individual game board only after both have responded. Provisions are made for E to transmit false feedback.     

A Simon effect for depth in three-dimensional displays

We investigated whether the Simon effect occurs for the depth dimension in a 3-dimensional display. In Experiment 1, participants executed discriminative responses to 2 stimuli, a cross and a sphere, both 3-dimensional, which were perceived to be located near or far with respect to the participant's body. The response keys were located near and far along the participant's midline. Apparent stimulus spatial location (near or far) was irrelevant to the task. Results showed a depth Simon effect, attributable to the apparent stimulus spatial location. Experiment 2 replicated Experiment 1 with a different procedure. The 2 stimuli, a triangle and a rectangle, were 2-dimensional and were perceived as being located near or far from the participant's midline; the response keys were located near and far along the participant's midline. Results showed again the depth Simon effect. Experiment 3 was a control condition in which the 2 stimuli, drawings of a lamp and of a chair, had the same size, regardless of whether they appeared to be near or far. The depth Simon effect was replicated. A distribution analysis on data of Experiment 3 showed that the Simon effect increased as reaction times became longer. In Experiment 4, the position of the 2 stimuli, a circle and a cross, varied on the horizontal (right or left) dimension, whereas the position of the 2 responses varied along the depth (near or far) dimension. No Simon effect was found.     

A rudimentary touch input device for visual displays

An inexpensive and simple device that can be fitted to existing computer visual display units and that gives a limited touch input capability is described. Small transparent acrylic pieces are held in front of the CRT by stiff wires attached to microswitches. The device has proved useful in the provision of computer-assisted instruction for young children.     

Adaptive user displays for intelligent tutoring software.

Intelligent tutoring software (ITS) holds great promise for K-12 instruction. Yet it is difficult to obtain rich information about users that can be used in realistic educational delivery settings--public school classrooms--in which eye tracking and other user sensing technologies are not suitable. We are pursuing three "cheap and cheerful" strategies to meet this challenge in the context of an ITS for high school math instruction. First, we use detailed representations of student cognitive skills, including tasks to assess individual users' proficiency with abstract reasoning, proficiency with simple math facts and computational skill, and spatial ability. Second, we are using data mining and machine learning algorithms to identify instructional sequences that have been effective with previous students, and to use these patterns to make decisions about current students. Third, we are integrating a simple focus-of-attention tracking system into the software, using inexpensive, web cameras. This coarse-grained information can be used to time the display of multimedia hints, explanations, and examples when the user is actually looking at the screen, and to diagnose causes of problem-solving errors. The ultimate goal is to create non-intrusive software that can adapt the display of instructional information in real time to the user's cognitive strengths, motivation, and attention.     

A rotator for X/Y oscilloscope displays

A simple and relatively inexpensive electronic circuit is described that will generate the Cartesian coordinates of a rotated display for both the X- and Y-axes of a conventional oscilloscope type of display monitor. The device will rotate the display through fixed angles and possesses the merits of very low intrinsic noise and extremely high speeds of response. It is particularly suited for computer control of stimulus orientation in psychophysical investigations of spatial contrast vision.