The effects of masking on vibrotactile temporal summation in the detection of sinusoidal and noise signals.

Thresholds for the detection of vibrotactile signals of varied duration applied to the thenar eminence were measured in the absence of and in the presence of a masking stimulus. Signals were 250- and 500-Hz sinusoids and noise bursts with bandwidth limited to 250-1000 Hz. The masking stimulus was either a 250-Hz sinusoid, which was presented in phase with the signal when it was sinusoidal, or noise. Changes in threshold as a function of changes in signal duration were found which were predicted accurately from Zwislocki's theory [J. Acoust. Soc. Am. 32, 1046-1060 (1960)] of temporal summation when the signal was detected by the Pacinian channel, but not when it was detected by a non-Pacinian channel (NP). However, when either the signal or the masking stimulus or both were noise, NP thresholds were affected by changes in signal duration. Only when the signal and masking stimuli were both sinusoids were NP thresholds independent of signal duration. It is concluded that signal duration effects in the NP channel are not due to temporal integration, but rather to increases in information about the signal content provided to the subject as exposure duration is increased.

Posttraining D1 receptor blockade impairs odor conditioning in neonatal rats.

Rat pups that were exposed to a novel anise odor paired with tactile stimulation (stroking the skin with a paint brush) received injections of either saline or the dopamine D1 receptor antagonist (+/-)-SKF 83566 (0.1 mg/kg) before conditioning or immediately after conditioning. Animals that received the drug either before or after training showed less approach to the conditioned odor during the testing period 24 hr later than did animals that received the vehicle. Posttraining administration of the D2 receptor antagonist spiperone (0.1 mg/kg) did not affect subsequent approach to the conditioned odor, suggesting a selective effect of D1 receptor blockade. The impairment in learning by the administration of (+/-)-SKF 83566 before conditioning was reversed by the injection of the dopamine receptor agonist apomorphine (0.1 mg/kg) immediately after conditioning. Posttraining D1 receptor activation appears necessary for normal odor conditioning in rat pups.