Concurrent variation of response bias and sensitivity in an operant-psychophysical test

The yes-no signal detection procedure was applied to a single-response operant paradigm in which rats discriminated between a standard auditory intensity and attenuated comparison values. The payoff matrix was symmetrical (with reinforcing brain stimulation for correct detections and brief time-out for errors), but signal probability and intensity differences were varied to generate a family of isobias and isosensitivity functions. The d’ parameter remained fairly constant across a wide range of bias levels. Isobias functions deviated from a strict matching strategy as discrimination difficulty increased, although an orderly relation was maintained between signal probability value and the degree and direction of response bias.     

Auditory evoked brain responses: Intensity functions from bipolar human scalp recordings

Average evoked brain responses were computed from four simultaneous recordings during binaural tone stimulation at 10 intensity levels. Amplitudes and latencies were measured for the prominent components, and linear regression coefficients were computed. The results indicate that the sensitivity of the evoked response to stimulus intensity is dependent upon the selection of the appropriate measure. Linear amplitude functions were demonstrated. Additional research relating these responses to psychophysical measures is suggested.     

Successive luminance difference thresholds and brightness as a function of the interstimulus interval and durations of successive flashes

Monocular,successive luminance difference thresholds (ΔI) and brightness matches (PSE) were obtained by the method of constant stimuli for two flashes successively presented to the same retinal area. Variations in interstimulus interval first-flash duration,and second-flash duration were the independent variables investigated. ΔI decreased as a function of ISI,while PSE remained relatively uninfluenced. An intensity-duration reciprocity was observed with increases in either first- or second-flash duration. Equal increases in duration of both flashes led to a constant value of ΔI. A Broca-Sulzer effect was also noted. In another study, a 10-msec, variable-luminance Standard was followed after 500 msec by either a 10-msec or a 320-msec test flash that was compared to the Standard. The results indicated that the rate of change of brightness with changes in luminance of the Standard was faster for the 10-msec flash than for the 320-msec flash. The rate-of-change hypothesis would predict that the 10-msec flash should have the smaller ΔI. The results for two Ss indicated the opposite: AI was smaller for 320-msec than for 10-msec flashes. A modification of the hypothesis was suggested such that it may be the energy increment (Δlt) required for detection that is related to the rate at which brightness changes with energy.     

The effect of forced choice on color discrimination

Color discrimination ability was measured at four spectral regions usually named blue, green, yellow, and red. Two methods, temporal forced-choice and phenomenal report, were compared. Data suggest that for color discrimination, phenomenal report is a preferable technique.     

Two types of short-term visual storage

Seven-letter words were flashed repetitively at various durations above and below the recognition threshold for single flashes. One form of a short-term storage effect was studied by measuring the interstimulus interval between flashes at which S reported that the stimulus became phenomenally discontinuous in time. Storage times reached a maximum of about 300 msec in this task. A second form of storage effect was measured by decreasing the interstimulus interval until S could correctly recognize a repeated stimulus whose duration was below the single-flash recognition threshold; this effect extended to 900 msec in some cases. Each of these effects was reliably obtained for both rare and frequent words. Both forms of storage were increased by providing a dark rather than a lighted adapting field between presentations of the test stimulus. Implications for Information processing of brief displays are discussed.     

A Bayesian prediction of four-look recognition performance from one-look data

The hypothesis that a human O’s (S’s) performance in a visual recognition task can be modelled by Bayes’ theorem was investigated. Two Ss were run for 40 experimental sessions each. Their task was to specify the direction of the gap of tachistoscopically presented Landolt rings (Cs). There were four possible gap directions, and two experimental conditions. In one condition, S responded after each stimulus presentation. In the other, a fixed-observation condition, Ss responded after four consecutive presentations of a C. Exposure durations were such that performance under both conditions was greater than chance, but less than unity. Predictions of four-look performance from one-look data were made. Overall hit rates were predicted closely. The entire pattern of each S’s four-look data was also predicted reasonably well. Further tests of the model are currently under way.     

Über Wahrnehmungsverhalten beim 8- bis 10wöchigen Säugling

Zusammenfassung Im Rahmen einer Systemtheorie des Verhaltens und der Persönlichkeit und auf dem Hintergrund der Ergebnisse der Berner Längsschnittuntersuchungen wird eine Hypothese über die Genese der Wahrnehmung entwickelt, wonach die frühesten Wahrnehmungen im wesentlichen Verarbeitungen der Reizwirkungen in einer von zwei Klassen von Verhaltenssystemen sind, nämlich der Abwendung und Selbstsicherung (A-Systeme) bzw. der Zuwendung zur Außenwelt (Z-Systeme).In einem Experiment mit 8-, 9- und l0wöchigen Säuglingen wurde das Wahrnehmungsverhalten in Abhängigkeit von verschiedenen Reizfiguren, von der individuellen Eigenart und vom Aktivationsniveau des Kindes mit Hilfe eines Zeitstichprobenverfahrens beobachtet. Der auf die Differenzierung zwischen den verschiedenen Reizfiguren entfallende Varianzanteil steigt mit zunehmendem Alter an, während die Wirkung der autonomen Aktivationsprozesse allmählich zurücktritt. Mit 10 Wochen kann eine geordnete Form oder gute Gestalt leichter verarbeitet werden als eine mehr zufällige Form.Einige Probleme im Zusammenhang mit Annahmen, Methoden und Ergebnissen des Experiments werden diskutiert, darunter die Theorie der Formwahrnehmung, die Genese von Subjekt- und Objektsystem und die beschränkte Bedeutung der Methode der bevorzugten Fixierung in der Erforschung der Säuglingswahrnehmung.

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Summary Within the framework of a System Theory of behavior and personality and against the background of the results of the Bernese Longitudinal Studies, a hypothesis of the genesis of perception is developed. It states that the earliest perceptions are essentially integrations of the effects of stimuli into one of two classes of behavioral systems, viz. withdrawal and self-preservation (A-systems) or, respectively, approach to the outer world (Z-systems).The perceptual behavior of 8-, 9-, and 10-week-old infants as a function of different stimulus forms, individuality, and activation level was observed by means of a time-sampling rating method. The proportion of variance accounted for by the differences between stimuli was found to increase with age; at the same time the effect of autonomic activation processes was decreasing. At the age of 10 weeks the infant can work up an orderly form or good Gestalt more readily than a more irregularly-shaped form.Some problems in connection with the assumptions, methods, and results of the study are then discussed, including form perception theory, the genesis of subject- and object-system, and some restriction of the method of preferred fixation in the study of infant perception.

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Gegenwärtig als Canada Council Postdoctoral Fellow an der York University in Toronto, Ont., Canada. Der Verfasser möchte seinem verehrten Lehrer Richard Meili seinen herzlichen Dank für die Anregung dieser Arbeit ausdrücken.