John Harsh

Time of day, repeated testing, and interblock interval effects on P300 amplitude

Time of day, repeated testing, and interblock interval effects on P300 amplitude were investigated. Subjects (N = 50) were tested using a standard oddball paradigm in either morning or afternoon sessions consisting of six test blocks per session. Amplitude of P300 was significantly higher in the morning than in the afternoon for all test blocks. In addition, amplitude of P300 habituated across test blocks from a mean of 9.59 microV on Block 1 to a mean of 4.98 microV on Block 6. Inserting a one-hour interval between Blocks 2 and 3 attenuated the rate of habituation. The results indicate that time of day, repeated testing, and interblock intervals affect P300 amplitude. Amplitude changes due to time of day may reflect circadian variations in cognitive resources indexed by the P300 component, while decrements due to repeated testing may reflect changes in allocation of resources across test sessions.

A concurrent assessment of the positive and negative properties of a signaled shock schedule

A choice and a conditioned suppression procedure were used to assess concurrently the positive and negative properties of stimuli within a signaled shock schedule, Occasional shocks were presented to Ss responding on a variable-interval food schedule. Ss could choose whether shocks occurred alone or whether they were preceded by a 1-min signal. All Ss chose the signaled shock condition over the unsignaled one, even though food reinforced responding in the presence of the signal was suppressed. Rate of responding for food varied across stimulus conditions, with the lowest rate in the presence of the signal and the highest rate in its absence. An intermediate rate occurred under the unsignaled shock schedule. A safety analysis was applied to the data.

Choosing between fixed time and variable time shock

Abstract Two experiments are reported dealing with choice of fixed or variable time shock schedules with and without signals. Response independent shock was presented on either a fixed-time or a variable-time schedule and subjects could change from one condition to the other for short periods after which the initial condition was automatically reinstated. In the first experiment shocks for both schedules were either unsignalled (6 subjects) or signalled (3 subjects) and all subjects changed from a schedule of variable-time shock to a fixed-time one. Subjects that were given the opportunity to change in the reverse direction did not do so. Opposite findings were obtained in the second experiment (7 subjects) comparing unsignalled fixed-time shock with signalled variable-time shock. Six of the seven subjects changed from the fixed-time schedule to the signalled variable-time one but not the reverse. The data were considered consistent with an analysis of choice based on the reinforcing value of discriminable shock-free periods.

Preference for signaled over unsignaled shock schedules: A reply to Furedy and Biederman

A portion of the literature concerning choice between signaled and unsignaled shock is reviewed. Based on this literature, several of the conclusions of Furedy and Biederman are challenged. Contrary to their conclusions, most researchers found a marked preference for the signaled shock condition whether shock was unscrambled, scrambled, or presented through surface electrodes.

Behavioral responsivity during recovery sleep

Previous research has shown that REM-deprived subjects are more likely than non-REM-deprived subjects to perform an operant response during subsequent REM sleep when punishment (full awakening) for failure to respond was used. The present study used the same punishment procedure while attempting to extend these findings to other sleep stages. Response latencies were compared for six subjects under each of two conditions: Normal sleep occurring from 2300 to 0700 and recovery sleep occurring from 0700 to 1300 after 24 hr of continuous wakefulness. Alpha activity, EMG increases, stage shifts, and body movements were assessed to determine the amount of arousal associated with behavioral responding under both conditions. In general, response latencies lengthened during recovery sleep indicating a diminished ability to respond while no differences in arousal were evident.