An adaptive procedure for rapid and efficient psychophysical testing is described. PEST (Parameter Estimation by Sequential Testing) was designed with maximally efficient trial-by-trial sequential decisions at each stimulus level, in a sequence which tends to converge on a selected target level. An appendix introduces an approach to measuring test efficiency as applied to psychophysical testing problems.

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Modafinil is an alerting substance that is considered safer than amphetamine with fewer side effects. Although modafinil has been used successfully to treat narcolepsy, relatively little is known about its ability to ameliorate fatigue and declines in mental performance due to sleep deprivation (SD) in a normal population. Forty-one military subjects received either 300 mg of modafinil, 20 mg of d-amphetamine, or placebo on 3 separate occasions during 64 hours of continuous cognitive work and sleep loss. Three drug treatments were given: at 23.30 hours and 05.30 hours during the first and second SD nights, respectively, and once at 15.30 hours during the third day of continuous work. Subjective estimates of mood, fatigue and sleepiness, as well as objective measures of reaction time, logical reasoning and short-term memory clearly showed better performance with both modafinil and amphetamine relative to placebo. Both modafinil and amphetamine maintained or increased body temperature compared to the natural circadian cycle observed in the placebo group. Also, from subject debriefs at the end of the study, modafinil elicited fewer side-effects than amphetamine, although more than the placebo group. Modafinil appears to be a good alternative to amphetamine for counteracting the debilitating mood and cognitive effects of sleep loss during sustained operations.

Previous experimental data on the roughness of grooved aluminum tiles provide a data base against which to test theories of roughness perception. A model based on the static deformation of the skin to.uching the stimulus tile is developed, and 11 parameters of the deformation are individually compared with the experimental data. All parameters were tested first in an approximate way, and then the better parameters were recalculated in a more exact manner. Three parameters, the depth to which the finger penetrates the groove, the cross-sectional area of the finger within the groove, and the cross-sectional area of the deviation of the skin from its resting position, all predict the roughness well as a function of finger force and groove width. The last of the three predicts roughness best as a function of land width, and is tentatively preferred as "the stimulus for roughness." All predictions from the static model indicate that variation of the coefficient of friction between skin and tile should have little or no effect. This counterintuitive prediction was confirmed by an experiment.Although psychophysics has been with us for over a century, there has been little discussion and no agreement on what constitutes the stimulus for roughness. There are two probable reasons for this lack: stimuli graded in an appropriate physical dimension are hard to manufacture, and knowledge of the tactile receptor systems and their functions is quite limited. There is so little agreement on the stimulus for roughness that the present authors were able to engage in a difference of opinion with their co-author in a recent chapter on texture perception (Taylor, Lederman, & Gibson, 1973). Gibson claimed that the perceived roughness of a surface depended on the frequency of vibration induced by the passage of the finger over the surface, while Taylor and Lederman held that vibratory energy, rather than its frequency, was responsible. The present paper introduces the hypothesis that neither vibratory frequency nor vibratory energy is the stimulus for perceived roughness; the deformation of the skin rather than the energy involved in the deformation is the important factor.

Until recently, most psychophysical experiments have studied sensory mechanisms involved in processing signals that vary along a single dimension. Under ordinary circumstances, however, the sensory system must operate in an environment where incoming signals vary along many different dimensions and often must deal with signals occurring simultaneously in different sensory modalities. In this report, we explore the question of how an O's performance on a set of simple discrimination tasks is affected by requiring the 0 to perform a number of these tasks at the same time.

MANY STUDIES (reviewed by Taylor, 1962) have indicated that there is consistency in the choice of meanings given to nonsense syllables by different people. This consistency, known as phonetic symbolism, has been attributed to qualities inherent in the sounds themselves. For example, Newman (1933) suggested that nonsense syllables with the vowel i are perceived as smaller than similar syllables with the vowel U, because of the higher pitch, or smaller vocal cavity associated with i. Any hypothesis of this nature leads to the prediction, to date untested, that the symbolic values of sounds must be similar in all languages. The present paper reports an experiment in which the symbolic values of nonsense syllables were determined for four unrelated languages on four different dimensions of meaning. Also reported are two preliminary experiments using English-speaking subjects, in which several factors affecting phonetic symbolism, and relevant to the design of die main experiment, were tested. PROCEDUREThe present investigation is analytical in the tradition of Sapir (1929) and Newman (1933). There were three experiments, in which the same general procedure was used, with same differences according to the specific requirements of the particular experiments. In each experiment the test material was composed of CVC (consonant-vowel-consonant) nonsense syllables mimeographed on three sheets of paper. A test booklet was made by stapling a page of instructions in front of the three randomly ordered pages of CVC syllables.In each experiment S was required to rate each syllable on some dimension of meaning, such as warmth or size, using a five-point rating scale. To rate a syllable S made a check mark on one of five dashes which followed each syllable. The S was reminded of the dimension to be rated, and the direction of his rating task with such an illustration as "small large" on the top of each test sheet There was no time limit for the task. For the purpose of statistical analysis, the five-point rating scale was used without transformation throughout the experiments. 1 The study reported here is based on part of the doctoral dissertation submitted by the senior author to the Johns Hopkins University. The authors wish to express thengratitude to Dr. James Deese for his valuable assistance.

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A previously proposed upper bound on the performance of psychophysical techniques that attempt to determine points on psychometric functions is shown to be a least upper bound. The existence of a realizable technique (the Robbins-Monro process) which asymptotically attains the performance of the proposed ideal shows that this ideal provides an appropriate basis from which to calculate the absolute as opposed to relative efficiency of real psychophysical measurement techniques. The concept of incremental efficiency is introduced. It is shown to be useful in analyzing the performance of measurement techniques when the initial uncertainty of the estimate, often ignored in simulation studies, is neither infinite nor zero, and to permit independent assessment of the efficiency of separate portions of a measurement process.