Accommodation fatigue and dark focus: The effects of accommodation-free visual work as assessed by two psychophysical methods

Past studies of accommodation fatigue have yielded inconsistent results, partly because they have not used direct measures of accommodation, and partly because they may have been based on a misleading conception of the nature of accommodation. The dual-innervation theory of accommodation suggests that the resting position of accommodation may be neuromuscular rather than just muscular, and that it lies not at optical infinity, as assumed by older conceptions, but at some intermediate position (dark focus). Among the predictions that may be deduced from this theory is that long-term visual work not requiring active accommodation will not induce fatigue. The present study involved continuous measurements of dark focus for 10 young adults over a 3-h period, using the laser optometer with two psychophysical procedures Ibracketing and staircase. Consistent with the prediction, no changes in dark focus were found, in spite of the demanding visual task. Furthermore, it was found that both psychophysical methods yielded essentially identical results. The practical and theoretical implications of these results are discussed, and recommendations are given regarding situations in which each of the psychophysical methods is likely to be most useful.     

Choice reaction time with a random foreperiod

Choice reaction latencies were measured at three different a priori probabilities for two stimulus alternatives. Unlike the results of some other studies, the mean latency of a given response was nearly the same whether the response was correct or incorrect. The discriminable stimuli were a 1000- or a 1700-Hz tone presented at 70 dB SPL. Latencies and standard deviations, based on about 17,000 observations, are reported for three observers. The data are compared with predictions of the optimum sequential model of Wald and Stone and two modifications of that random-walk model, one proposed by Link and Heath and the other proposed by Laming. Fast-guess analyses were also carried out. The three-parameter version of either the sequential or the modified random-walk models provided reasonably accurate predictions of the mean data for each observer. The parameters estimated by the fast-guess analysis were unrealistic. There are three obvious differences between this experiment and most previous choice reaction-time experiments. First is stimulus modality#x2014;we used an auditory signal, whereas most of the previous studies used a visual signal. Second, the observers practiced more in this experiment than in most previous experiments. Finally, there was a random foreperiod with a heavy penalty for anticipations. One or more of these factors is the probable reason for the discrepancy between our results and those of previous studies.     

Duplex perception with musical stimuli

Duplex perception, a phenomenon previously demonstrated for speech stimuli, is demonstrated here for musical stimuli. In the first experiment, major and minor chords are produced by dichotic fusion of two simultaneous piano notes presented to one ear (perfect fifth) with a “natural” or “flat” single note presented to the opposite ear. Musically trained subjects perceive simultaneously both the single tone and a fused (major or minor) chord. The chords are labeled more consistently than the single notes, even though the fused chords differ solely in terms of the contralateral notes. In a second experiment, using pure tones in place of piano notes, other musically trained subjects individually exhibited categorical perception for either the fused chord or the single tones, but never for both types of stimuli. The duplex phenomenon is discussed in terms of its implications for its specific component modes of perception.     

An Apple II package for computer-assisted telephone interviewing

This paper describes an Apple II (an Apple-compatible) microcomputer package for a computer-assisted telephone interviewing (CATI) system. This system generates random telephone numbers within any number of exchanges that the user supplies, automatically dials the telephone, prompts the interviewer with each question, and records and permanently saves each response. It also provides a printed copy of the collected data by frequency of response in each question category. The Apple II CATI package is readily available, inexpensive, and easy to program in the BASIC language.     

A generalization of Kristof's theorem on the trace of certain matrix products

Kristof has derived a theorem on the maximum and minimum of the trace of matrix products of the form \(X_1 \hat \Gamma _1 X_2 \hat \Gamma _2 \cdots X_n \hat \Gamma _n\) where the matrices \(\hat \Gamma _i\) are diagonal and fixed and theX _i vary unrestrictedly and independently over the set of orthonormal matrices. The theorem is a useful tool in deriving maxima and minima of matrix trace functions subject to orthogonality constraints. The present paper contains a generalization of Kristof's theorem to the case where theX _i are merely required to be submatrices of orthonormal matrices and to have a specified maximum rank. The generalized theorem contains the Schwarz inequality as a special case. Various examples from the psychometric literature, illustrating the practical use of the generalized theorem, are discussed.     

Categorization reaction time,category structure,and category size in semantic memory using artificial categories

This study examined the effects of category structure and category size on categorization reaction time, artificial categories being used to obtain greater experimental control than is usually found in semantic memory research. Four artificial categories varying in structure (hierarchical and nonhierarchical) and size (8 or 16 instances) were introduced to 20 adolescent subjects over a 12-week period by means of stories, exercises, and discussions. Significantly longer categorization reaction times were required for instances from the hierarchical categories, but no set size effect was found. The application of clustering and multidimensional scaling procedures to subjects’ free recall data revealed that subjects had acquired the hierarchical structures but imposed their own structures on the other categories. These findings were interpreted within a spreading activation framework.     

Social networks,information-seeking,and the utilization of services

Voluntary participation by low-income and/ar high-risk populations in prevention-oriented human service programs is minimal and dropout rates are high. Examination of social networks as they relate to information-seeking and utilization behavior may provide a source of understanding. Two investigations are reported. The results of Study 1 indicate that high-risk referred women with denser networks attended fewer parent group sessions than did those whose networks were less dense and that the more contact a woman had with her kin, the fewer parent group sessions she attended. The results of Study 2 indicate that in a sample of low-income women participating in a supplementary food program, those women whose networks were characterized by lower density and less frequent kin contact were more likely to pursue professional child-rearing information and advice than women in denser, more kin-involved networks. In addition, a significant interaction between one's sense of competence as a parent and the structure of one's network was found to determine the overall frequency of information seeking.     

The generalization of the effects of a cognitive-behavioral treatment program for aggressive children

A cognitive-behavioral treatment program for aggressive children was assessed using 12 outcome measures classified into five categories which reflected a continuum of generalization of treatment effects. From a summer daycamp 41 children, ages 7 through 12, were selected based on aggressive behavior displayed during the first week of camp. They were randomly assigned to either a treatment group or a nontreatment control group. Treatment consisted of four weeks of coping-skills training using behavioral rehearsal and self-instruction training. Considering all 12 measures, treatment was found effective (F=2.90, p < .01). The most meaningful results included improved interpersonal problem-solving skills and a decrease in being disciplined for fighting. No changes were found, however, in physical or verbal aggression and in peer rating of aggression. Modest support for the effectiveness of these treatment procedures was identified, although caution is needed in considering their clinical utility. Further research and application appear justified.