The vestibulo-collic reflex represents a promising test for evaluating the integrity of otolith function. We have investigated the threshold of this response in a group of normal subjects, and the effect of a conductive hearing loss. A positive response was recorded in 31 of 32 normal subjects. The threshold of the vestibulo-collic reflex varied from 80 to 97 dBHL in these subjects with a 95% response rate at a threshold at 96 dBHL. A total of 23 ears with a conductive hearing loss in 17 patients were also investigated. The average conductive hearing loss (at 0.5, 1, 2 and 4 kHz) ranged from 8.75 to 40 dBHL (average 24.46 dBHL). A positive response was recorded in only two ears. Therefore, the vestibulo-collic reflex has a high stimulus threshold which is dependant on reliable transmission of the click stimulus to the inner ear thus limiting is clinical use.

The variability in behavior has frequently been assessed using a measure known as the U-value. Of concern in the present paper were the limits and constraints on U-value as a measure of variability. The relation between the U-value and aspects of variability was examined using three sets of simulated data. Our analysis demonstrates that the U-value as a measure of variability on its own fails to capture repetitive patterns in the sequence of responding. The U-value was shown to reflect the evenness of the distributions of responses across the categories/options used; however, when the number of categories actually used by the participant differed from the total number available, the relation between U-values and the number of categories allocated with responses was shown to be non-linear. It was also shown that the same value of U can represent different levels of evenness in response distributions over categories, depending on the number of categories/options actually used. These constraints and limitations are discussed in relation to how researchers might report on behavioral variability.

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Many diverse species have demonstrated interval timing, the ability to respond appropriately to time in the range of seconds to minutes, suggesting that an ability to time is adaptive. The peak procedure is a common method of studying interval time perception. In the peak procedure, animals experience a mix of fixed-interval (FI) and extinction (EXT) trials. On EXT trials, responding typically increases to a peak at the time the FI schedule would normally deliver reinforcers before decreasing. Responding on different FI schedules within the peak procedure has been found to conform to Weber's law, whereby response variability is proportional to the length of the fixed interval. We conducted possibly the first investigation of the timing abilities of a marsupial common to Australia and New Zealand, the brushtail possum (Trichosurus vulpecula), using FI 15-, 30-, and 60-s schedules of reinforcement in the peak procedure. Response rates on EXT trials peaked at the time of usual reinforcer delivery, decreasing at longer time intervals, and were well fit by 3-parameter Gaussian curves, demonstrating the ability of possums to respond to time-based stimuli. Coefficients of variation suggested that the ability of possums to time was less accurate than that of mammals, but similar to that of birds, invertebrates, and reptiles. Coefficients of variation did not differ consistently over increasing FI intervals, showing that timing responses of possums likely conforms to the scalar property of timing also shown by other species. (PsycINFO Database Record