On-line brain stimulation: Measurement of threshold of reinforcement

This program and interface for a small computer (PDP8/e) performs the following operations: generates and delivers constant current stimulation to the brain of an animal, monitors electrical resistance at the stimulating electrode, and calculates the threshold of reinforcement based upon the frequency of characteristic pauses in the animal’s responding.     

The time it takes to make veridical size and distance judgments

Two experiments measuring the time it takes to make veridical size judgments under normal (unreduced) conditions of viewing showed that RT tended to increase with increases in viewing distance between 122 and 305 cm, even for targets subtending the same visual angle at all distances. Two experiments measuring the time it takes to judge distance under the same conditions did not reveal any difference in RT as a function of the extent-of-distance judged. Established accounts of size perception do not suggest an explanation of these findings.     

Temporal summation at the warmth threshold

Threshold levels for warmth aroused by infrared irradiation were measured in sLx Ss at durations between 0.05 and 10 sec. Beyond a critical duration of about a second, the threshold does not depend on duration. Below critical duration time t trades for irradiance ? by the formula ? = kt^?0.82. That these properties do not depend much on areal extent of stimulation was demonstrated by a study that compared temporal summation for two different areas of the same S’s skin. Individual differences in apparent absolute sensitivity were explored under the rubric of the theory of signal detection.     

Reaction time as a measure of summation of warmth

Reaction time (RT) to radiant heat applied to the forehead and to the back was found to decrease monotonically as a function of two variables: intensity (flux density) and areal extent of stimulation. Intensity and area can thus be traded one for the other to preserve a constant RT. It has previously been shown that intensity and area can be traded to preserve a constant degree of apparent warmth, as determined by magnitude estimation. RT and magnitude estimation therefore agree in showing that the warmth sense displays spatial summation, and both show that summation is very great. They also agree in showing that the foreheadés sensitivity greatly exceeds the backés, and the exact trading rules revealed by magnitude estimation and RT agree well at low and moderate intensities.     

Appropriateness of anxiety and drive for affiliation

Anxiety was induced in first/only born and later born subjects by the threatened injection of a harmless drug. Perceived appropriateness of the induced anxiety was manipulated by the experimenter's suggestion that anxiety over an injection was either perfectly natural (appropriate condition) or to be found only in rather nervous and effeminate men (inappropriate condition). The results indicated that the anxiety induction was successful, but that the perceived appropriateness of the anxiety determined the tendency to affiliate. Subjects in the appropriate condition showed a significantly greater tendency to affiliate than did subjects in the inappropriate condition. Birth order was related to anxiety on one of two measures, but was not implicated in the determination of the affiliative tendency.     

The equivalence of target and nontarget processing in visual search

A comparison of a forced-choice visual search task with an item recognition task did not support Neisser’s (1967) hypothesis of a preattentive stage that processes targets and nontargets differentially. In the forced-choice condition, Ss indicated which of two items in a visual display was a target; in item recognition, Ss determined whether or not the single item in the visual display was a target. The size of the memorized set of possible targets was varied from one to six items for both tasks. Latencies increased linearly with memory set size in both conditions; the slopes for forced choice and item recognition were 41.8 and 27.9 msec per item, respectively. The ratio of 1.38 between the two slopes was well fit by Sternberg’s (1967) item recognition model, which predicts a ratio of 1.50.