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At least 1,621 records · Page 90Linked to original sources
PubMed1993

Ideal observer for discrimination of the global direction of dynamic random-dot stimuli.

Random-dot cinematograms in which each dot's successive movements are randomly drawn from a Gaussian distribution of directions can produce a percept of global coherent motion in a single direction. Discrimination of global direction was measured for various exposure durations, stimulus areas, and dot densities and bandwidths of the distribution of directions. Increasing the duration produced a greater improvement in performance than did increasing either the area or the density. Performance decreased as the distribution bandwidth increased. An ideal-observer model was developed, and the absolute efficiency for human direction discrimination was evaluated. Efficiencies were highest at large distribution bandwidths, with average efficiencies reaching 35%. A local-global noise model of direction discrimination, based on the ideal-observer model, containing a spatial and temporal integration limit as well as internal noise, was found to fit the human data well. The utility of ideal-observer analyses for psychophysical tasks and the interpretation of efficiencies is discussed.

Discriminant Analysis↗
PubMed1985

Effect of static-noise and grating masks on detection and identification of grating targets.

Ability to detect grating targets and to distinguish between gratings of different spatial frequencies was measured in the presence of static-noise masks and grating masks. Static noise reduces detection and identification in similar fashion, although the effect on detection is greater under some conditions. Grating masks alter identification more than detection, but the effect on identification is reduced when distinctive beat patterns are present to aid identification.

Attention↗
PubMed1985

Spatial-frequency masking and Birdsall's theorem.

We measured the masking of a spatial 4-cycle/deg sinusoid in the presence of both random and sinusoidal masks. Subjects used a variety of detection strategies, depending on psychophysical technique and familiarity with the mask. Some strategies produce Weber's-law behavior and appear formally equivalent to identification tasks; we hypothesize that these exemplify the operation of Birdsall's theorem. Other strategies produce power-law behavior and are more like the simpler detection task. Our results suggest that criterion change (commonly uncontrolled in masking studies) can produce an unacceptably large bias in the results.

Attention↗
PubMed2006

Visual and nonvisual contributions to three-dimensional heading selectivity in the medial superior temporal area.

Robust perception of self-motion requires integration of visual motion signals with nonvisual cues. Neurons in the dorsal subdivision of the medial superior temporal area (MSTd) may be involved in this sensory integration, because they respond selectively to global patterns of optic flow, as well as translational motion in darkness. Using a virtual-reality system, we have characterized the three-dimensional (3D) tuning of MSTd neurons to heading directions defined by optic flow alone, inertial motion alone, and congruent combinations of the two cues. Among 255 MSTd neurons, 98% exhibited significant 3D heading tuning in response to optic flow, whereas 64% were selective for heading defined by inertial motion. Heading preferences for visual and inertial motion could be aligned but were just as frequently opposite. Moreover, heading selectivity in response to congruent visual/vestibular stimulation was typically weaker than that obtained using optic flow alone, and heading preferences under congruent stimulation were dominated by the visual input. Thus, MSTd neurons generally did not integrate visual and nonvisual cues to achieve better heading selectivity. A simple two-layer neural network, which received eye-centered visual inputs and head-centered vestibular inputs, reproduced the major features of the MSTd data. The network was trained to compute heading in a head-centered reference frame under all stimulus conditions, such that it performed a selective reference-frame transformation of visual, but not vestibular, signals. The similarity between network hidden units and MSTd neurons suggests that MSTd may be an early stage of sensory convergence involved in transforming optic flow information into a (head-centered) reference frame that facilitates integration with vestibular signals.

Action Potentials↗
PubMed1989

The effect of repeated occasions of alcohol intoxication on two processes involved in the visual discrimination of movement.

The focus of this study was the effect of repeated episodes of alcohol intoxication on two processes involved in visual movement discrimination: visual sensitivity and decision-making. Four female subjects were asked to discriminate between a stationary light signal and one that changed position in the center of a dark visual field. Prior to each of 15 alcohol testing sessions, a dose of .66 ml of 95% USP ethanol per kg body weight was administered to each subject and BAL was sampled frequently within sessions. Differences in subjects' pre- and postalcohol performance were evaluated within the framework of a psychophysical model that mathematically characterizes the problem of movement discrimination and yields independent estimates of visual sensitivity and decisional aspects of subjects' performance. Evidence for specificity in the development of sensory versus decisional process tolerance to intoxication effects was found. The major result was that each subject made large and statistically reliable shifts in decisional criteria during the time course of the blood alcohol curve within alcohol testing sessions, even when visual sensitivity had adapted to alcohol intake effects. The results of this study illustrate the utility of tracing acute intake effects over repeated occasions of intoxication, and empirically testing subjects' assumed decisional strategies when modeling these effects.

Adult↗
PubMed1989

On the limits of the matching concept in monkeys (Cebus apella).

Two cebus monkeys, with many years of experience matching a variety of static visual stimuli (forms and colors) within a standard matching-to-sample paradigm, were trained to press a left lever when a pair of displayed static stimuli were the same and to press a right lever when they were different. After learning the same/different task, the monkeys were tested for transfer to dynamic visual stimuli (flashing versus steady green disks), with which they had no previous experience. Both failed to transfer to the dynamic stimuli. A third monkey, also with massive past experience matching static visual stimuli, was tested for transfer to the dynamic stimuli within our standard matching paradigm, and it, too, failed. All 3 subjects were unable to reach a moderate acquisition criterion despite as many as 52 sessions of training with the dynamic stimuli. These results provide further evidence that, in monkeys, the matching (or identity) concept has a very limited reach; they consequently do not support the view held by some theorists that an abstract matching concept based on physical similarity is a general endowment of animals.

Animals↗
PubMed1981

Effect of stimulus perspective on perception of oscillation.

8 groups of subjects, 10 per group, had 10 trials for each of two perceptual tasks. Subjects in each group viewed a rotating trapezoid at a constant speed at equal-interval angles of tilt (0 degrees, 30 degrees, 60 degrees, 90 degrees) and two directions of stimulus tilt (toward observer and parallel to observer). It was predicted that most reports of oscillatory perception would occur for parallel tilt at 0 degree and 90 degree angles of orientation. In addition, there would be a hypothesized decrease in perceived oscillations from 0 degrees to 90 degrees when the stimulus was tilted toward the observer. Both direction of stimulus tilt and angle of orientation were significant. Post hoc comparisons yielded reliable differences from the parallel tilt and tilt toward the observer. The evidence supports the position that veridical information processing in the trapezoid oscillatory illusion is a joint function of signal-detection capability and availability of perceptual cues.

Adult↗
PubMed1985

Nonveridical factors of visual perception and close following on the road.

Close following on the road, identified as contributing to accidents, may be partly explained as an involuntary response to nonveridical perceptual factors. These factors concern (a) underestimation of the driver's own speed and (b) incorrect estimations of the distance away and speed of the vehicle ahead of the driver.

Automobile Driving↗