Monaural and binaural audiogenic seizures in mice

The progression of sound-induced seizures was examined in unilaterally or bilaterally sensitized SJL/J mice tested either monaurally or binaurally. An unexpected right-side advantage for becoming susceptible to audiogenic seizure was observed. In addition, two distinct patterns of seizure progression were noted, a uniphasic sequence in which a single burst of running preceded the convulsion and a biphasic pattern with two such bursts. The biphasic progression is viewed to be the result of unilaterally initiated seizures and characteristically reached only a clonic level of severity. Uniphasic seizures are concluded to be the result of bilaterally initiated seizures and, when they occurred after more than 30 s of auditory stimulation, frequently reached a tonic level of intensity. The present results support the view that audiogenic seizures are characterized by precisely timed, sequential processes dependent upon the specific priming and test procedures employed.     

Changes in cochlear microphonic sensitivity after priming C57BL/6j mice at various ages for audiogenic seizures.

Groups of mice were briefly exposed to a one-octave band of noise at 14, 18, 28, 38, or 58 days of age. Five days later the groups were divided, and some mice were behaviorally tested for audiogenic seizures by reexposing them to the same sound. The round window cochlear microphonic potential was measured in the remaining animals and compared with that observed in unprimed control subjects. Seizure behavior occurred in all animals primed on Day 18 but rarely for subjects in the other age groups. Cochlear microphonic threshold curves in mice primed on Day 18 showed a 30-dB loss in sensitivity, while all other primed groups showed little change. These data were discussed in terms of the "disuse-supersensitivity" hypothesis previously proposed to account for the physiological effects of priming in mice.     

Social categorization as a function of priming

The present study investigates the effect of priming on the use of social categorizations. Using sex and race as stimulus categorizations, previous studies failed to confirm the hypothesis that priming one of the two available categorizations would enhance the use of the primed categorization relation to the not-primed categorization. As suggested by Stangor, Lynch, Duan and Glass (1992). a momentary increase in accessibility may be insufficient to further enhance the use of highly accessible categorizations like race and sex, but it may be expected that priming will increase the use of categorizations which are less habitually used in daily life. The results of the present experiment support the hypothesis that, when the stimulus categorizations are weakly accessible (university major, university town), the relative use of the previously primed categorizations does indeed increase, compared to the alternative, not-primed, categorization.     

Roles of anoxia and noise-induced hearing loss in the postictal refractory period for audiogenic seizures in mice.

The present series of experiments demonstrated a postictal refractory period for audiogenic seizures in DBA/2J mice, which was not related to hearing loss but apparently was related to anoxia. Unlike many previous studies, Experiment 1 controlled for the effects of noise exposure upon hearing sensitivity and demonstrated reduced susceptibility to subsequent audiogenic seizures for at least 1 hr after initial clonic-tonic convulsions. The postictal refractory period was shown to result from the occurrence of seizures per se, not from noise exposure alone. Experiment 2 demonstrated deficiencies of sensorimotor functions that accompanied reduced postictal seizure susceptibility. The two phenomena had similar time courses of recovery, which suggested a common mechanism, probably anoxia, associated with the initial convulsions. In support of this view, Experiment 3 showed that recovery from both phenomena was expedited by allowing subjects to breathe increased O2. The role of anoxia in fatal convulsions was suggested by the finding that subjects experiencing clonic-tonic convulsions in a high-O2 environment survived without exception. In contrast, seizures of air-breathing controls were almost always fatal. Taken together, the data indicate that the postictal reduced susceptibility to audiogenic seizures was closely related to metabolic depletion (in particular, anoxia). The pattern of recovery of susceptibility further suggests that the effects of anoxia impair the spread of seizure activity through the central nervous system, although the initiation of seizures is also affected for a short time.     

Weber fractions for weight and mass as a function of stimulus intensity

Laboratory simulations of weightlessness have shown that the Weber fraction for mass is higher than that for weight in the range 1000-7000 g. Experiments in the weightless conditions of orbital and parabolic flight have found the same at the 50 g level. To obtain measures at intermediate intensities, the Weber fractions for weight and mass were measured for 15 subjects at 50, 200 and 400 g. The stimuli were canisters suspended on strings. The subjects lifted them for the weight condition and swung them firmly sideways for the mass condition. The Weber fraction was higher for mass than for weight at all intensities, and increased at 50 g for both conditions. In a second mass condition, in which the subjects shook the cylinders within a loosely clenched hand, the Weber fraction remained almost constant at all intensities and was significantly smaller than for the firm swing method at 50 g. The differences in performance between conditions may be related to the continuity or intermittency of pressure information. Other explanations are discussed.     

Reaction time as a function of stimulus intensity for the monkey

Monkeys were trained to release a telegraph key in response to a visual or auditory stimulus. The latency of the key release response was measured for different stimulus intensities. In general, the relation between latency and intensity is inverse and exponential with greater variability of latency at the lower intensities. Some preliminary data involving differential reinforcement of short latencies are presented.     

Dissociating mere exposure and repetition priming as a function of word type

The mere exposure effect is defined as enhanced attitude toward a stimulus that has been repeatedly exposed. Repetition priming is defined as facilitated processing of a previously exposed stimulus. We conducted a direct comparison between the two phenomena to test the assumption that the mere exposure effect represents an example of repetition priming. In two experiments, having studied a set of words or nonwords, participants were given a repetition priming task (perceptual identification) or one of two mere exposure (affective liking or preference judgment) tasks. Repetition priming was obtained for both words and nonwords, but only nonwords produced a mere exposure effect. This demonstrates a key boundary for observing the mere exposure effect, one not readily accommodated by a perceptual representation systems (Tulving & Schacter, 1990) account, which assumes that both phenomena should show some sensitivity to nonwords and words.