Thurstone's discriminal processes fifty years later

Four issues are discussed concerning Thurstone's discriminal processes: the distributions governing the representation, the nature of the response decision rules, the relation of the mean representation to physical characteristics of the stimulus, and factors affecting the variance of the representation. A neural schema underlying the representation is proposed which involves samples in time of pulse trains on individual neural fibers, estimators of parameters of the several pulse trains, samples of neural fibers, and an aggregation of the estimates over the sample. The resulting aggregated estimate is the Thurstonian representation. Two estimators of pulse rate, which is monotonic with signal intensity, are timing and counting ratios and two methods of aggregation are averaging and maximizing. These lead to very different predictions in a speed-accuracy experiment; data indicate that both estimators are available and the aggregation is by averaging. Magnitude estimation data are then used both to illustrate an unusual response rule and to study the psychophysical law. In addition, the pattern of variability and correlation of magnitude estimates on successive trials is interpreted in terms of the sample size over which the aggregation takes place. Neural sample size is equated with selective attention, and is an important factor affecting the variability of the representation. It accounts for the magical number seven phenomenon in absolute identification and predicts the impact of nonuniform distributions of intensities on the absolute identification of two frequencies. 1977 Psychometric Society Presidential Address. This work was supported in part by a grant of the National Science Foundation to Harvard University. I wish to express my appreciation to S. Burbeck, D. M. Green, M. Shaw, and B. Wandell for their useful comments on an earlier draft of this paper.     

Individual magnitude estimates for various distributions of signal intensity

Magnitude estimates of loudness were collected for several variations in the schedule of signal presentations. For wide ranges (about 50 dB centered at 65 dB), the conditions were: random selection of 21 signals equally spaced in decibels, constrained selection so that each signal was used equally often but successive signals were always close together, constrained selection in which successive signals were always far apart, and random selection from a nonuniform distribution that consisted of two groups of equally spaced signals separated by a gap of 24 dB. In addition, two other ranges, 10 and 30 dB, were run with random selection of 21 equally spaced signals. The measures examined were: mean magnitude estimate as a function of signal intensity, coefficient of variation of the ratio of successive responses as a function of signal separation, and the correlation of the logarithm of successive responses as a function of signal separation. The basic question was whether all of the different schedules of signal presentation produce data that can be viewed as selections from appropriate regions of the 50-dB random signal selection data. To a degree, this was found, but with systematic exceptions.     

Reliability and validity of scores on the Slosson Auditory Perception Skills Screener

Psychometric characteristics of the Slosson Auditory Perception Skills Screener were studied using three independent samples of boys and girls ages 5-10 years (N= 1,170). Internal consistency of scores ranged from .83 to .90 for the total scale, while 30-day test-retest reliability was .82 (n=58). A convergent validity coefficient between the Slosson Auditory Perception Skills Screener and Test of Auditory Perceptual Skills-Revised Total Score was .59 (n=67, p<.05). Thus, scores derived from administration of the Slosson Auditory Perception Skills Screener had adequate internal consistency and temporal stability, as well as good convergent validity.     

Detection of auditory signals presented at random times,II

The paper includes experimental results obtained using two procedures in which signals are presented at random times. A simple three-stage theory consisting of a sensory process, followed by a response bias, and ending in a response process, involving a random delay, and that mayor may not have a memory, is compared with the data. The free-response procedure yielded data that could not be accounted for by a first version of the theory in which the crucial assumption about the response process was that once a response process is under way it locks out all further inputs until the response is made. Alternative models, including a race between response processes with the first response suppressing all others and a simple first-in first-out queue, were equally inadequate. On the assumption that the difficulties lie in the complexities of the response process when there are two or more inputs close in time, we decided to avoid these theoretical difficulties by using a modified reaction-time procedure. The initial results are encouraging. The tails of the latency distributions appear to be exponentially distributed and a theoretical prediction that two of the time constants should be the same appears to be supported. The major indications of difficulties are inconclusive evidence that the response bias parameter may not be constant and, possibly related, that the initial portion of the tails may overshoot the predicted value. In spite of the possible variation in the bias parameter, estimates of the signal-plus-noise to noise-alone parameters increase in a systematic manner with signal strength     

A SUPERVISION PROGRAM FOR INCREASING FUNCTIONAL ACTIVITIES FOR SEVERELY HANDICAPPED STUDENTS IN A RESIDENTIAL SETTING

This study was designed to increase the amount of time severely handicapped students living in a residential facility engaged in age-appropriate and functional activities. After a brief in-service training, a program involving instructions to supervisors and staff feedback was implemented in a multiple-baseline design across settings. Results showed that after the supervision program was implemented, the students' participation in activities increased. Further, these increases maintained when feedback was reduced from an average of 3 days a week during treatment, to once a month for a 5-month period.     

The Provision of Assistive Technology by Occupational Therapists Who Practice in Mental Health

The purpose of this study is to determine what assistive technology devices occupational therapists working in mental health settings use with their clients. Based on the literature, the authors expected that no tech and low tech assistive technology solutions are being used with clients in these settings even though high technology options are available for people with mental illness who have co-existing cognitive disabilities. The findings of the study reveal that indeed no tech and low tech interventions are most often used. Implications for professional development educational programs and further research are suggested.     

A solution to a problem raised in Luce and Marley (2005)

Luce and Marley [2005. Ranked additive utility representations of gambles: Old and new axiomatizations. Journal of Risk and Uncertainty, 30, 21-62] examined various relations between mathematical forms for the utility of joint receipt ⊕ of gambles and for the utility of uncertain gambles. Their assumptions lead to a bisymmetry functional equation which, when the gambles are ranked, is defined on a restricted domain. Maksa [1999. Solution of generalized bisymmetry type equations without surjectivity. Aequationes Mathematicae, 57, 50-74] solved the general case and Kocsis [2007. A bisymmetry equation on restricted domain. Aequationes Mathematicae, 73, 280-284] presents the solution for the ranked case. The latter solution allows us to solve open problem 5 in Luce and Marley (2005) by showing that the assumptions of their Theorem 19 for an order-preserving ranked additive utility (RAU) representation U imply that U is a ranked weighted utility (RWU) representation that is additive over ⊕.     

Computer- and internet-based psychotherapy interventions

Computers and Internet-based programs have great potential to make psychological assessment and treatment more cost-effective. Computer-assisted therapy appears to be as effective as face-to-face treatment for treating anxiety disorders and depression. Internet support groups also may be effective and have advantages over face-to-face therapy. However, research on this approach remains meager.