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Biomedical subjects

G Sperling

Publications and source records attributed to G Sperling.

At least 55 records · Page 3Linked to original sources
PubMed1987

Dynamics of automatic and controlled visual attention.

The time course of attention was experimentally observed using two kinds of stimuli: a cue to begin attending or to shift attention, and a stimulus to be attended. Precise measurements of the time course of attention show that it consists of two partially concurrent processes: a fast, effortless, automatic process that records the cue and its neighboring events; and a slower, effortful, controlled process that records the stimulus to be attended and its neighboring events.

Acoustic Stimulation↗
PubMed1987

Limits of visual communication: the effect of signal-to-noise ratio on the intelligibility of American Sign Language.

To determine the limits of human observers' ability to identify visually presented American Sign Language (ASL), the contrast s and the amount of additive noise n in dynamic ASL images were varied independently. Contrast was tested over a 4:1 range; the rms signal-to-noise ratios (s/n) investigated were s/n = 1/4, 1/2, 1, and infinity (which is used to designate the original, uncontaminated images). Fourteen deaf subjects were tested with an intelligibility test composed of 85 isolated ASL signs, each 2-3 sec in length. For these ASL signs (64 x 96 pixels, 30 frames/sec), subjects' performance asymptotes between s/n = 0.5 and 1.0; further increases in s/n do not improve intelligibility. Intelligibility was found to depend only on s/n and not on contrast. A formulation in terms of logistic functions was proposed to derive intelligibility of ASL signs from s/n, sign familiarity, and sign difficulty. Familiarity (ignorance) is represented by additive signal-correlated noise; it represents the likelihood of a subject's knowing a particular ASL sign, and it adds to s/n. Difficulty is represented by a multiplicative difficulty coefficient; it represents the perceptual vulnerability of an ASL sign to noise and it adds to log(s/n).

Adult↗
PubMed1986

Tradeoffs between stereopsis and proximity luminance covariance as determinants of perceived 3D structure.

A 2D polar projection of a 3D wire cube (Necker cube) in clockwise rotation can be perceived either veridically as a clockwise-rotating cube (rigid percept) or as a counterclockwise-rotating rubbery, truncated pyramid (nonrigid percept). The 3D percept is influenced by various cues: linear perspective, stereo disparity, and proximity-luminance covariance (PLC, the intensification of edges in proportion to their proximity to the observer). Perspective, by itself or in combination, is a very weak cue whereas PLC is a powerful cue [Schwartz and Sperling (1983) Bull. Psychon. Soc. 21, 456-458]. Here we determined psychometric functions for perceptual resolution in static displays and dynamic rotating displays (with and without a static preview) as determined by stereopsis and PLC in isolation and with both cues jointly, possibly in conflict. Stereopsis was the dominant cue in static displays and in most dynamic displays. When a static display preceded a dynamic display, it strongly influenced the subsequent dynamic percept. Perceptual resolution in all conditions was accurately described by a winner-take-all model in which the strength of evidence for each percept from different cues is simply algebraically added.

Depth Perception↗
PubMed1986

A signal-to-noise theory of the effects of luminance on picture memory: comment on Loftus.

In studies of picture memory, subjects typically view a sequence of pictures. Their memory is tested either after each picture is presented (short-term recall) or at the end of the sequence (long-term recall). The increase in performance as a function of picture viewing time defines "the rate of information acquisition." Loftus (1985) found that reducing the luminance of a picture reduces the rate at which information is acquired (for both short-term and long-term tests) and, for long viewing times, reduces the total amount of recall. The theory proposed here assumes that both of these effects are consequences of intrinsic noise in the visual system that becomes relatively more prominent as signal (picture luminance or contrast) is reduced. Noise shares a limited capacity channel with signal, and thus noise reduces the rate of information acquisition; noise, as well as signal, occupies space in memory, and thus noise reduces recall performance.

Attention↗
PubMed1985

Continuous measurement of visible persistence.

In the synchrony judgment paradigm, observers judge whether a click precedes or follows the onset of a light flash and, on other trials, whether or not a click precedes light termination. The interclick interval defines the duration of visible persistence. An elaboration of this method consists of two phases: In Phase 1, the luminance of a reference stimulus is psychophysically matched to the peak brightness of the test flash. Five luminance values between .1 and 1.0 of the reference stimulus are used subsequently. In Phase 2, a random one of the five reference stimuli, a test flash, and a click are presented; the observer judges whether the click occurred before or after the brightness of test flash reached the reference value (on onset trials) or decayed below it (on termination trials). This method was validated on 3 subjects with test stimuli whose luminance rises and decays slowly in time, and then was used to trace out the precise subjective rise and decay (temporal brightness response function) of brief flashes.

Acoustic Stimulation↗
PubMed1985

Three theories of stroboscopic motion detection.

The three theories derive from three different paradigms. Suprathreshold judgements of perceived quality of motion in multi-flash displays are modelled by space-time Fourier analysis of the motion stimulus. Stroboscopic motion is perceived as being different from real motion to the extent that the additional Fourier components in stroboscopic motion are detectable. Stroboscopic motion of dots along conflicting paths leads to perceptual competition. The theory to describe perceptual I solution derives and proves the uniqueness of strength functions computed only from the time and from the distance between successive points on each path. Time-strength and motion-strength add to determine path-strength; only the strongest path is perceived. Motion-direction detection in continuously drifting two-flash combinations of sinusoidal gratings is described by elaborated Reichardt detectors (ERDs) that compute the covariance of temporal events in two adjacent locations. Other apparently different, detectors that account for direction-detection data are shown to be equivalent to ERDs.

Light↗
PubMed1985

Elaborated Reichardt detectors.

The elaborated Reichardt detector (ERD) proposed by van Santen and Sperling [J. Opt. Soc. Am. A 1, 451 (1984)], based on Reichardt's motion detector [Z. Naturforsch. Teil B 12, 447 (1957)], is an opponent system of two mirror-image subunits. Each subunit receives inputs from two spatiotemporal filters (receptive fields), multiplies the filter outputs, and temporally integrates the product. Subunit outputs are algebraically subtracted to yield ERD output. ERD's can correctly indicate direction of motion of drifting sine waves of any spatial and temporal frequency. Here we prove that with a careful choice of either temporal or spatial filters, the subunits can themselves become quite similar or equivalent to the whole ERD; with suitably chosen filters, the ERD is equivalent to an elaborated version of a motion detector proposed by Watson and Ahumada [NASA Tech. Memo. 84352 (1983)]; and for every choice of filters, the ERD is fully equivalent to the detector proposed by Adelson and Bergen [J. Opt. Soc. Am. A 2, 284-299 (1985)]. Some equivalences between the motion detection (in x, t) by ERD's and spatial pattern detection (in x, y) are demonstrated. The responses of the ERD and its variants to drifting sinusoidal gratings, to other sinusoidally modulated stimuli (on-off gratings, counterphase flicker), and to combinations of sinusoids are derived and compared with data. ERD responses to two-frame motion displays are derived, and several new experimental predictions are tested experimentally.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1984

Temporal covariance model of human motion perception.

We propose a model of direction-sensitive units in human vision. It is a modified and elaborated version of a model by Reichardt [Z. Naturforsch . Teil B 12, 447 (1957)]. The model is applied to threshold experiments in which subjects view adjacent vertical bars with independently (typically sinusoidally), temporally modulated luminances. The subject must report whether the patterns moved to the left or to the right. According to the model, a basic motion-detecting unit consists of two subunits tuned to opposite directions. Each performs a spatial and temporal linear filtering of its input; outputs of the filters are multiplied, and the multiplied output is integrated (for a time that is long relative to the modulation period). The model's output consists of the difference between the subunit outputs. Direction of movement is indicated by the sign of the model output. Mathematical analysis of the model yielded several predictions that were confirmed experimentally. Specifically, we found that (1) performance with complex patterns can be predicted by spatiotemporal Fourier analysis that results in the segregation and linear addition in the output for different temporal frequencies; (2) under special conditions, performance depends on the product of adjacent bar amplitudes, offering strong support for the multiplication principle; (3) performance is unaffected by addition of stationary patterns; and (4) addition of homogeneous flicker normally produces no effect but under special conditions reverses perceived direction. These and other results confirm our model and reject several other models, including Reichardt 's original model.

Fourier Analysis↗
PubMed1984

[Comparison of the effects of piracetam and methohexital on cerebral energy metabolism].

Several authors suggest an influence of piracetam on brain energy metabolism. Therefore, we examined the effect of this drug on the levels of high-energy phosphates, glucose, some metabolites of glycolysis and free amino acids in the rat brain under normoxic, ischemic and postischemic conditions. In order to eliminate peripheral effects on the cerebral metabolism the isolated perfused rat brain was used as a model for this study. Methohexital was also administered for demonstrating protective effects on energy metabolism under the experimental conditions employed. The barbiturate, not piracetam, reduced the recovery time of the EEG after 1.5 or 2 min of ischemia. The depletion of energy reserves after the ischemic periods was diminished by methohexital but not by piracetam. The substrate and metabolite levels removed faster to the control levels under methohexital in the postischemic period whereas the piracetam treated brains did not differ from the controls. The subchronical treatment of rats in vivo with piracetam only caused a slightly smaller increase in the cerebral lactate concentration after anoxic periods. These results do not suggest an acute effect of piracetam on rat brain energy metabolism whereas the barbiturate methohexital may protect the brain against ischemic damage in a certain extent.

Amino Acids↗
PubMed1982

Relationship between brain mitochondrial hexokinase and neuronal function: comparable effects of 2-deoxy-D-glucose and thiopental.

Mitochondrially bound brain hexokinase is solubilized by anesthetics and this effect has been suggested to contribute to anesthesia. In the present investigation the influence of the metabolic inhibitor 2-deoxy-D-glucose (2-DOG) was studied. An isolated rat brain preparation was used to avoid the contribution of peripheral reactions. Isolated rat brains were perfused for 45 min with media containing 4 mmol/l glucose, 10 mmol/l 2-DOG and/or 0.4 mmol/l thiopental. The EEG was monitored and acetylcholine, 2-DOG and its 6-phosphate, as well as the intracellular distribution of hexokinase activity were determined in brain tissue. Soluble hexokinase activity in brain cortex was enhanced by 2-DOG, as also by thiopental, and even more pronounced by both drugs used together, Results from in vitro experiments suggest that solubilization of mitochondrial hexokinase after 2-DOG is mediated by intracellularly accumulated 2-DOG-6-phosphate. 2-DOG produced a significant impairment of neuronal activity, revealing EEG patterns similar to those caused by thiopental anesthesia. Cortical acetylcholine levels were elevated by 2-DOG, as well as by thiopental, and again both drugs showed an additive effect when used in combination. This effect which may be the result of an inhibition of acetylcholine release, was also detectable in mice in vivo after 5 g 2-DOG/kg i.p., whereas the same dose of 3-O-methylglucose had no effect. The results provide further evidence that mitochondrial hexokinase may be involved in the relationship between cerebral metabolism and brain function.

Animals↗
PubMed1981

Effects of thiopental on regulatory mechanisms of brain energy metabolism.

After administration of thiopental to artificially ventilated rats, the EEG, cerebral metabolism, intracellular distribution of hexokinase activity and the thiopental concentration in brain was measured. Considering the EEG changes, the time course of thiopental action was divided into an initial stage with increased beta activity and a following second stage with reduced beta activity. The glucose-6-phosphate concentration significantly increased in the first stage and fell again to the control level with the beginning of the second stage. Furthermore, during the second stage the glucose level increased and the hexokinase activity shifted from the mitochondrially bound form to the soluble form. From these results the following conclusions were drawn: Phosphofructokinase activity appeared inhibited only during the initial stage. During the second stage comparable to the stage of surgical anesthesia, thiopental solubilizes bound hexokinase activity inhibiting thereby energy metabolism.

Amino Acids↗
PubMed1980

[Acrodermatitis enteropathica: a treatable disease today].

Acrodermatitis enteropathica was diagnosed in a girl at the age of 13 months. The clinical symptoms of the patient conformed to the known features of Acrodermatitis enteropathica. The gstrointestinal symptoms were not present. Previous to therapy the serum-zinc levels of the patient were markedly decreased. Following substitution with Zincaspartat the clinical condition improved and the serum-zinc levels returned to normal. The aetiology, pathogenesis, clinical course and the therapy of the disease are reported.

Acrodermatitis↗
PubMed1980

Perceptual delay: a consequence of metacontrast and apparent motion.

Temporal-order judgments were used to demonstrate that a later visual stimulus can delay the perception of an earlier one when the two stimuli together produce the phenomenon of metacontrast or of apparent motion. The perceptual delay is the same for movement and metacontrast and for one or two characters appearing to move or to be masked.

Humans↗