A programmable circuit for varying light intensity

An inexpensive circuit is described for the control of light intensity. The control is obtained by a method that produces no color changes and may be programmed by any system that can express itself in four-digit binary numbers.     

Perceiving the intensity of light

The relationship between luminance (i.e., the photometric intensity of light) and its perception (i.e., sensations of lightness or brightness) has long been a puzzle. In addition to the mystery of why these perceptual qualities do not scale with luminance in any simple way, "illusions" such as simultaneous brightness contrast, Mach bands, Craik-O'Brien-Cornsweet edge effects, and the Chubb-Sperling-Solomon illusion have all generated much interest but no generally accepted explanation. The authors review evidence that the full range of this perceptual phenomenology can be rationalized in terms of an empirical theory of vision. The implication of these observations is that perceptions of lightness and brightness are generated according to the probability distributions of the possible sources of luminance values in stimuli that are inevitably ambiguous.     

Negative affect varying in motivational intensity influences scope of memory

Emotions influence cognitive processes involved in memory. While some research has suggested that cognitive scope is determined by affective valence, recent models of emotion–cognition interactions suggest that motivational intensity, rather than valence, influences these processes. The present research was designed to clarify how negative affects differing in motivational intensity impact memory for centrally or peripherally presented information. Experiments 1 & 2 found that, relative to a neutral condition, high intensity negative affect (anger) enhances memory for centrally presented information. Experiment 3 replicated this effect using another high intensity negative affect (threat). Experiment 4 extended this by finding that, relative to a neutral condition, low intensity negative affect (sadness) enhanced memory for peripherally presented information. Finally, in Experiment 5, the effects of sadness and threat on scope of memory were directly compared, finding that threat narrowed scope of memory, while sadness broadened scope of memory. Together, these results provide additional support for the motivational dimensional model of cognitive scope, in that high intensity emotions narrow cognitive scope, while low intensity emotions broaden cognitive scope.     

Reaction time to the second of two shortly spaced auditory signals both varying in intensity

Six subjects participated in a reaction time (RT) task in which the stimulus events consisted of two sinusoidal waves presented in close succession. The leading stimulus (S₁) had a duration of 25 msec while the binary reaction stimulus (S₂) was 250 msec. Presentation of the interstimulus interval (ISI) was irregular. S₁ as well as S₂ varied in intensity and were assigned randomly the values of 45, 68, 85 and 105 db (SPL). RT to S₂ was examined as a function of the intensity of both stimuli. Generally RT varied inversely with the intensity of S₁ and the downward gradient of RT with ISI became steepened at least for ISIs shorter than 200–250 msec. Concerning S₂, RT grew shorter as the intensity increased up to 85 db. Probably due to startle, RT tended to lengthen at S₂ = 105 db. When both S₁ and S₂ were 105 db the startle effect upon RT seemed most evident. Then the elevation in RT took place at especially those ISIs for which he fastest RTs might have been expected (about 200 msec). For the remaining intensities no interaction between S₁ and S₂ upon RT was found even for the shortest ISIs, implying that the effects of S₁ and S₂ intensities upon RT were independent.     

Discrimination of intensity differences carried on formant transitions varying in extent and duration

Dorman (1974) found that small-intensity differences carried on the initial portions of consonantvowel syllables were not discriminable. Similar differences carried on steady-state vowels and on isolated formant transitions, however, were readily discriminable. He interpreted the difference between the first and latter conditions as a phonetic effect. Yet Pastore, Ahroon, Wolz, Puleo, and Berger (1975) found similar results using sine-wave analogs to Dorman’s stimuli. They concluded that the effect is not phonetic, and that it is attributable to simple backward masking. The present studies observed the discriminability of intensity differences carried on formant transitions varying in extent and duration. Results support the conclusion of Pastore et al. to the extent that the effect is clearly not phonetic. However, these results and others suggest that simple peripheral backward masking is not a likely cause; instead, recognition masking may be involved. Moreover, the finding that phonetic-like processes occur elsewhere in audition does not necessarily impugn the existence of a speech processor; phonemic and phonological processes remain, as yet, unmatched.     

A system for controlling the light output of a monochromator by any simple function and for temporally modulating the intensity

This paper describes an apparatus that controls the output of a monochromator so that the energies in each waveband can be equated according to any desired function. A photocell monitors the light from the monochromator and provides a feedback to the power supply driving the lamp. A function generatoris mechanically linked to the monochromator’s wavelength drive and provides the function for correcting the output spectrum. Once set, the light output remains constant even if the bulb ages or is replaced. If desired, a sinusoidalripple of variable frequency and amplitude can be imposed on the mean intensity of the light.     

Lingual vibrotactile threshold alterations in response to varying stimulation levels of intensity and duration.

Lingual vibrotactile thresholds were obtained at a frequency of 250 Hz by using an ascending-continuous series of stimulation during five sessions. Each of three adult male Ss attended a control session which included a prescribed period of constant tongue positioning, a pre-experimental session where the mean of six thresholds was obtained as a basis of further testing, and three experimental sessions. In the experimental sessions vibrotactile thresholds after exposure to vibratory stimulation of varying levels of intensity and duration were obtained. The findings of the control session reflected a slight pattern of decreased lingual sensitivity indicative of the influential factor of constant maintenance of tongue positioning. Results from the experimental sessions demonstrated shifts toward progressively decreased lingual sensitivity after exposure to vibratory signals of increased levels of intensity and duration. A recovery phase to near-normal sensitivity followed each stimulus presentation.     

The overshadowing of background stimuli: Some effects of varying amounts of training and ucs intensity

Two experiments investigated the capacity of a nominal CS to overshadow background stimuli. Rats received CS-shock pairings in one compartment of a double compartment apparatus. After training the shock compartment was represented, but in the absence of both the CS and shock. Overshadowing was then assessed by measuring rats' latency to enter this compartment. If rats readily entered the shock compartment this indicated that the background cues in that compartment had acquired little or no associative strength during training, and overshadowing was therefore inferred. If however rats avoided the shock compartment, then this indicated that the background stimuli must have become aversive during training, and overshadowing could not then be inferred. In both experiments it was found that the capacity of a CS to overshadow background stimuli was directly related to the amount of training given. The experiments also showed that this capacity is inversely related to shock intensity. The results are discussed in terms of Rescorla and Wagner's (1972) model of conditioning.     

Escape behavior under continuous reinforcement as a function of aversive light intensity

In 11 male albino rats, lever-pressing responses, maintained under a CRF escape schedule with light as the aversive stimulus, were examined at each of five intensities, viz., 2.5, 18, 105, 190, and 386 ft-C. The function relating reciprocal of latency of the escape response to aversive light intensity passed through a maximum.     

Contrasting two accounts of anxiety-linked attentional bias: selective attention to varying levels of stimulus threat intensity

Previous research has established that clinical anxiety patients and nonclinical populations with high levels of anxiety vulnerability characteristically orient attention toward moderately threatening stimuli. In contrast, populations with low levels of anxiety vulnerability typically orient attention away from such stimuli. The differing experimental predictions generated by 2 classes of hypothetical explanation for this anxiety-linked attentional discrepancy were tested, using attentional probe methodology to compare the attentional responses of high and low trait anxious individuals to facial stimuli of differing threat intensities. The results support the view that all individuals orient attention away from mildly threatening stimuli and toward strongly threatening stimuli, with differences in anxiety vulnerability reflecting the intensity of stimulus threat required to elicit the attentional vigilance response.     

Contributions to the history of psychology: LXXXII. Authors, perceived color, and light intensity.

Two eponyms, the Purkinje phenomenon and the Bezold-Brücke phenomenon, are sometimes confused in discussions of the effect of light intensity upon perceived color. The former refers to a change in apparent brightness; the latter refers to a change in perceived hue.