Multiple observation tasks are often used to investigate observers’ abilities to combine information from different sources or observations. This paper discusses a method for assessing the relative weight given to each observation. First, a theorem that derives the relative weights is stated. A technique for estimating relative weights is then illustrated by analyzing data from a multiple-tone task. In this task, observers listen to a sample of tones drawn from one of two distributions and decide which distribution was sampled. Results show that observers integrate information nonoptimally, attaching greater weight to the first and/or last observations than to observations occurring in the middle of the sequence. The generality of the technique is discussed.

A sequence of seven tones, sampled from one of two distributions differing in mean frequency, is presented to observers who try to report which distribution was sampled. Estimates are obtained of the weight or importance given to each tone as a function of its temporal position. In five experiments, the reliability of the information is varied by changing the variance of the distributions; tones with high reliability are sampled from distributions with relatively small variance, whereas tones with low reliability are sampled from distributions with relatively large variance. Results show that the observations are weighted more efficiently when the tones have equal rather than unequal reliability, and when the most reliable tones have the greater intensity. Additional results show that the most intense tones often receive the greatest weight, even when those tones have the least reliability.

Treatments that interfere with animals' short-term retention (e.g., in delayed matching-tosample] were studied using a spatial memory task. Rats performed in an eight-arm radial maze in which choosing each arm without repetition was the optimal behavior. Performances were interrupted between fourth and fifth choices for a delay of 15 sec to 2 min. A variety of events occurring during the delay interval did not disrupt memories for prior choices (as assessed by the accuracy of postdelay choices). The ineffective treatments inc1uded variations in visual and auditory environments, removal from the maze, food consumed during the delay, a distinctive odor added to the maze, or combinations of these manipulations. Additionally, performance on another spatial task (a four-arm maze) during the delay between Choices 4 and 5 did not interfere with performance in the eight-arm maze. These findings suggest that rats' memories for spatiallocations are immune to retroactive interference, at least within the range of conditions reported, and that the rat can successfully segregate memories for spatial locations established in different contexts.

The COSS analysis suggested by Berg [B. G. Berg, J. Acoust. Soc. Am. 86, 1743-1746 (1989)] is applied to a profile listening task. The listener's task is to detect an increment in the level of the middle component of an n-component spectrum. The overall level of the components is randomly selected from a 20-dB range on each presentation; thus the detection task is essentially one of detecting a change in spectral shape. To implement the COSS analysis, a small perturbation in level is added to each component of the complex. COSS functions are generated from these perturbations, and the spectral weight that the listener assigns to each component is estimated. Data are reported for n = 3, 5, and 11 components and for perturbations with standard deviations of 0.5, 1, and 2 dB. The estimated weights are similar to those derived for an optimum detector; namely, the level at the signal component is compared with the average level of the nonsignal components. This result supports the view that profile analysis involves an across-channel comparison process. The pattern of weights also provides insight into differences among listeners. In a separate experiment, the spectral weights of a very poor profile listener are estimated, and the pattern of the weights suggests reasons for the inferior detection performance.

The authors argue mathematically that a common, power-function model of the just-noticeable difference in stimulus intensities is logically inconsistent with an exponent other than 1 in those frequent situations in which a particular averaging over experimental conditions has taken place. The authors show that an alternative power-law model, one which does not share this logical inconsistency, provides a good fit to many well-known, psychoacoustic intensity discrimination data. They also show that the exponent in this alternative model must be nonconstant with the discrimination criterion in experiments implementing this averaging of data.