Dichotic sequence discrimination: The effect of continued practice

Summary Dichotic sequence discrimination was studied by means of a three-alternative forced-choice method. Two of the alternatives (same) consisted of a single pair of dichotic clicks with the stimulus at one ear preceding the stimulus at the other ear by a given temporal separation (e.g., R-t-L). One of the alternatives consisted of a single pair of clicks with the opposite sequence (e.g., L-t-R). The subjects' task was to discriminate between the different and the same dichotic pairs. The results indicate that discrimination is a nonmonotonic function of t, i.e., V- or U-shaped, with high levels at both short and long temporal separations (t=2 and 4 ms and t=64 and 96 ms) and with lower levels of discrimination for intermediate ts. A second experiment was performed to study the effect of continued practice by subjects trained in dichotic sequence discrimination for ts 4 and 64 ms (high discrimination levels) and for t=16 ms (low discrimination level). There was no systematic trend towards improvement over 8 blocks of 50 trials for each t. Discrimination levels of these ts did not differ between Experiments 1 and 2.Dr. Babkoff is spending the 1979–1981 academic year at the Walter Reed Army Institute of Research, Department of Military Medical Psychophysiology, Forest Glen Annex, Building 189, Washington, D.C. 20012, USAThe experiments were conducted at the Bar-Ilan University, Ramat-Gan, Israel. The authors would like to thank the Bar-Ilan Research Committee for making funds available to conduct the experimentsThis material has been reviewed by the Walter Reed Army Institute of Research, and there is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense     

The impact of cognitive interference on performance during prolonged sleep loss

Summary A study was conducted on the effects of off-task cognitions on performance during sleep deprivation. Subjects answered the Thought Occurrence Questionnaire, assessing their proneness to engage in off-task cognitions, and were deprived of sleep for 72 hours, during which they performed a variety of tasks including visual discrimination and three versions of a logical reasoning task in which cognitive load was varied systematically. In addition, every day subjects answered the Cognitive Interference Questionnaire, which taps off-task cognitions during the experiment. Results indicated that subjects who habitually engage in off-task cognitions performed worse during 72 hours of sleep loss than subjects who do not engage in such distracting activities. In addition, it was found that the engagement in off-task cognitions increased during the 72 hours of sleep loss and such an engagement was related to deficits in performance accuracy. The mechanisms of off-task cognitions and sleep loss underlying these effects are discussed.     

Partial integration of single electrocutaneous pulses

Psychometric functions generated by single eleetroeutaneous stimuli yielded a median coefficient of variation ( σ/μ ) of 0.23. These data are consistent with other psychometric data recently reported by us which yielded σ/μ ratios of this size. The data are discussed and related to conflicting data reported in the recent literature indicating coefficients of variation for this mode of stimulation which are only 1/3 as large. Evidence is presented for partial temporal summation (time-intensity reciprocity) for electrocutaneous stimuli ranging from 175 to 610 microseconds. The data are best fitted by the equation I x t^a = k, where a is approximately 0.57. This equation and exponent also fit summation data reported by the same authors who report finding steep psychometric functions. Clearly, then, the mechanism responsible for the very limited temporal summation found for eleetrocutaneous stimulation and the mechanism responsible for very steep psychometric functions are not identical. The discussion also includes speculation regarding possible mechanisms and suggestions for research.     

Dichotic sequence discrimination: The effect of stimulus intensity and background noise level

Dichotic temporal discrimination of clicks over the range of separation of 2 ≤ Δt ≤ 96 msec is nonmonotonic, being V- or U-shaped with two maxima, one at very short separations (?t≤4 msec) and one at long separations (Δt ≥ 64 msec). Decreasing the level of the stimuli or increasing the level of background noise results in an overall decrement in discrimination level and a widening of the base of the function to make it more U-shaped. These effects are expressed in shorter Δt thresholds for the left limb of the function and longer Δt thresholds for the right limb of the function     

Dynamic changes in work/rest duty cycles in a study of sleep deprivation

The effects of moderate workload and 72 h of sleep deprivation were studied using a modified continuous-performance paradigm. Ten subjects were tested hourly on a number of perceptual and cognitive tasks designed to require approximately 30 min to complete, with the remainder of each hour free. As sleep deprivation continued, the average time on task increased at an accelerating rate. The rate of increase differed among tasks, with longer tasks showing greater absolute and relative increases than shorter ones. Such increases confound sleep deprivation and workload effects. In this paper, we compare the advantages and disadvantages of several experimental paradigms; describe details of the present design; and discuss methodological problems associated with separating the interactions of sleep deprivation, workload, and circadian variation with performance.     

Monotonic and rhythmic influences: a challenge for sleep deprivation research

There are both monotonic and rhythmic factors in the patterns of change seen in physiological, psychological, and performance variables during sleep deprivation. These monotonic and rhythmic factors can be orthogonal, or they may interact with each other, with various task variables, or both. The importance of separating the rhythmic from the monotonic factors and of elucidating their interactions is discussed. Experimental methods and types of analysis appropriate to evaluating these factors are examined, with special emphasis on the complex demodulation time series analysis applied to group or individual subject data. The discussion is accompanied by data illustrations. It is suggested that sleep deprivation research should be designed so as to generate physiological and behavioral data that include information on both monotonic and rhythmic factors, the nature and extent of their interaction, and how they interrelate with systematically manipulated independent variables.     

Response probability and response latency to threshold electrocutaneous stimuli

A comparison was made between two measures of somatosensory sensitivity, response probability, and reaction time to electrocutaneous constant current pulses of 350-microsec duration. The psychometric functions are steeper than those obtained for other sensory modalities. Similarly, the reaction-time/intensity functions are also steeper than those obtained in other modalities, i.e., larger decreases in reaction time as a function of small increases in stimulus intensity. Ss exposed to a broad stimulus range, including high intensities, yield psychometric and reaction time functions displaced into a higher intensity region than when they are exposed to a narrow low-intensity range of stimuli. The data are discussed in terms of a decision-theory model of reaction time.     

Discrimination of equal-energy,equally detectable auditory stimuli

Summary Two experiments were conducted. In the first experiment, psychometric functions were generated for tones of 988 Hz of 16 and 64 ms duration. The results indicate that for detection, both durations are within critical duration, i.e., equal detection levels were obtained for stimuli of equal energy. In the second experiment, pairs of equal-energy, equally detectable tones of 16 and 64 ms were used to test the ability of subjects to discriminate between them. The results indicate that equal-energy, equally detectable tones of different intensities and durations are discriminable from one another although the durations do not exceed the limits of complete reciprocity when the response measure is detection. Two different interpretations are presented and discussed.The authors would like to thank Jacob Gutgold and Miriam Izaks for their aid with the equipment and experiment.     

The role of tone duration in dichotic temporal order judgment

Over the past two decades, a number of studies have been based on the dichotic temporal order judgment (TOJ) paradigm, to compare auditory temporal processing in various subpopulations to that of young, normal controls. The reported estimates of dichotic TOJ thresholds, expressed as the interstimulus intervals (ISIs) for 75 % accuracy among the controls, have varied. In the present study, we examined the influence of tone duration, within the 10- to 40-msec range, on dichotic TOJ accuracy and threshold. The results indicated that increases in either ISI or tone duration increased dichotic TOJ accuracy similarly, implying that changes in tone duration may affect dichotic TOJs simply by adding to the delay between onset of the tone at the lead ear and onset of the tone at the lag ear. The dichotic TOJ thresholds from three published studies that had used tones as stimuli and the dichotic thresholds from the present study all fell within 0.5 standard deviations from the theoretical line of a 10-msec reduction in threshold for every 10-msec increase in tone duration. When the dichotic TOJ threshold data from the present study and from the published studies were converted to stimulus onset asynchronies (SOAs) and plotted as a function of tone duration, they fell very close to or on a zero-slope line, indicating that when ISI and duration are summed to yield an SOA, dichotic TOJ thresholds are invariant to tone duration within the range of 10–40 msec.