An inherent problem in certain constant-current stimulators

A basic and potentially dangerous problem that may occur in the use of triggered constant-current generators for stimulation is discussed in the general case. A solution with schematic illustration is presented for one specific constant-current generator, the CCS-1A manufactured by Electronics of Life Sciences, Inc.     

EMG waveform duration: A validation method for the surface electromyogram

The electromyogram (EMG) recorded with surface electrodes was examined using a triggered oscilloscope technique. When all but the high-amplitude waveforms in a given segment of activity were excluded from analysis, it was found that the duration of the remaining waveforms was specific to the muscle that produced them. That is, waveforms of a given duration were recorded whenever conventional indices-observable contraction, joint movement. needle recordings-showed activity in a specific muscle. This led to the suggestion that waveform duration might be used to validate the surface EMG. The suggestion. which is limited by the need to control posture and electrode placement, both of which may influence waveform duration, was illustrated in application to psychological research.     

Non-interaction of ventromedial and lateral hypothalamic mechanisms in the regulation of feeding and hoarding behaviour in the rat

Lesions of the hypothalamic ventromedial nucleus (VMN) led to an immediate increase in food intake but not to any increase in hoarding activity. Later, when subjects were very obese, they failed to hoard even in response to a 16-hr. deprivation schedule, although this schedule did produce hoarding if body weights were held at, or were brought down to, preoperative levels. These results indicate that the lateral hypothalamic mechanism responsible for hoarding and feeding responds to long-term nutritional factors, and that it is not directly affected by the short-term satiety mechanisms in the VMN. These findings support the hypothesis (a) that even “non-physiological” activities (e.g. hoarding, exploration) are motivated by physiological needs, and (b) that the reason these activities do not ordinarily covary with physiological drives is that, unlike the physiological drives, they are not subject to inhibition by the hypothalamic satiety mechanisms.     

The time it takes to imagine1

Stanley and Furedy (1966), using the paired-comparisons technique, reported that under conditions where size constancy held, Emmert’s law failed as distance increased beyond 90 in. Experiment 1, designed to check this report with a shorter-duration induction flash, did not yield 90 in. as the point of failure. However, although complete size constancy for direct images was again obtained, the results did not unambiguously suggest strict proportionality between afterimage size and distance. To allow a less ambiguous assessment of proportionality, Experiment 2 used magnitude-estimation procedures. Distance estimates were completely veridical, but afterimage size varied only linearly, and not proportionally, with apparent distance. It was concluded the Boring (1940) was mistaken in his attempt to reduce size constancy and Emmert’s law to the same principle.     

Redistributing control between the elements of a compound stimulus

Twenty-eight pigeons were given discrimination training. Four groups were run in which for 0, 2, 4 and 9 sessions of training colour was an irrelevant cue and tone was relevant. Generalization tests were given in extinction; the training colour (C₁) and another colour (C₂) were presented with tone (T) and noise (N). Responding to these four stimulus combinations, TC₁, TC₂, NC₁ and NC₂, allowed the assessment of control by colour and tone. A reduction of control by colour and an increase in control by tone were found to be positively related to the amount of training with colour irrelevant. Tests showed a strong inverse relationship between control by colour and tone.     

Taste sensitivity in infrahuman species: Use of a genetic model to test the validity of alternative measures

In a genetic analysis of PTC taste sensitivity of mice, Ss were presented tap water and a PTC solution in a two-choice situation. A preference index was used as a measure of taste sensitivity, assuming that ability to taste would lead to avoidance, i.e., negative preference. This assumption, however, lead to the rejection of seven Ss who preferred the test solution. Due to the undesirability of deleting Ss, the data were reanalyzed, using an alternative index of taste sensitivity that required no assumption concerning the hedonic quality of the test solution. Information regarding the inheritance of taste sensitivity to PTC provided the validating criterion for this measure.     

Fixed interval schedules and delay of reinforcement

In a fixed interval schedule of reinforcement the only responses to be reinforced are those made when a certain time interval has elapsed since the previous reinforcement. The behaviour of three rats on such a schedule was compared with their behaviour on a schedule where a response made at any time during the interval was reinforced by setting up a reward which was delivered when the interval had elapsed. Response rates were higher in the ordinary fixed interval schedule than in its modified version, and it is argued that this rules out attempts to explain the maintenance of fixed interval performance by delayed reinforcement. Despite the clear difference in response rates, there was considerable similarity between the post-reinforcement pauses developed in the two schedules, and this suggests that pausing is influenced more by temporal than by response contingencies.