The Effect o f Alcohol on Human Information Processing Rate

Transcription

1 The Effect o f Alcohol on Human Information Processing Rate Herbert Moskowitz1 and James Murray Epidemiological data indicate that the presence of alcohol greatly increases the probability of accidents in driving. It is not clear what behavioral mechanisms are affected by alcohol to produce the impairment of skills performance which underlies these accidents. It has been suggested that the impairment of skills performance by alcohol, especially at lower dose levels, occurs due to effects on central information processes rather than peripheral sensory or motor mechanisms (4). Evidence that one of the central factors affected by alcohol is the rate of information processing is supported by studies demonstrating an increase in response latency under alcohol when conditions demand processing of considerable information from the stimulus configuration (5, 7). While these studies included controls to demonstrate that the increased latencies could not be ascribed solely to sensory and/or motor factors, the relative contribution of sensory, motor and central mechanisms to the latency increases could not be separately determined. The present study employs the technique of backward masking of a visual stimulus to give a more direct estimate of the effect of alcohol on one stage of central information processing time without confounding by sensory or motor processing delay. The technique is based upon recent research which presents strong evidence that there are three memory systems within the human organism, a very brief sensory information storage system known also as iconic memory, a short-term memory system (STM), and a long-term memory system (3, 9). Typically, when a visual stimulus is present briefly (in a range of under 200 msec) the subjective duration is longer than the physical stimulus duration due to iconic memory, which can be conceptualized as a rapidly fading visual image. The duration of this image depends on various factors, such as the character of the pre- and post-stimulus visual fields, but typically lasts less than one second (10). If the information contained in the visual image is to be retained further, it must be transformed into the form necessary for retention by the STM system, which does not store information visually (3). Readout of information from the sensory information store into STM requires time. The length of time required can be determined by use of the backward masking technique. In this technique, the visual target stimulus (TS) is presented very briefly 1 School of Engineering, University of California at Los Angeles, Los Angeles, California

2 400 H. Moskowitz and J. Murray (15 msec) and is followed after some inter-stimulus interval (ISI) by a visual masking stimulus (MS) which interferes with the visual image of the first stimulus and thereby stops the transfer of TS data into STM. Since the MS interferes with the visual image of the TS, the time available for reading out the information in the visual image is the period from onset of TS to onset of MS, i.e., the ISI plus the TS duration, which is then the effective or subjective duration of the visual image. By varying the ISI and determining the relative amounts of information readout of the image, the rate of this stage of information processing is measured. This study compared the effects of three dose levels of alcohol upon the amount of information readout of the'visual image. The possibility that any change in performance could be due to an effect upon sensory input was controlled by two factors. Since any delay of sensory transmission time by alcohol would affect the TS and MS equally, leaving the effective duration of the TS unchanged, such an effect would not confound the results. Secondly, a condition was included where no MS followed the TS, which gives the subject more than ample time to read out all the information contained in the TS. Under the no-mask condition, any evidence of impairment of performance by alcohol would indicate the presence of another source of alcohol impairment than a decrement of central processing time. Thus it controls for both sensory and motor confounding factors as well as against a possible effect on shortterm memory. METHOD The subjects were 12 males, aged years, with 20/20 vision corrected or uncorrected Ṡtimuli were presented in a 3-field tachistoscope with a cm viewing distance. The test stimulus card was presented in one field, the masking stimulus card in the second field, and the third field contained a card with a fixation point. Test stimuli were white cards with four black capital letters in a 10.8 cm wide horizontal row subtending 6.8 degrees of visual arc. Letters for each card were chosen at random without replacement from the alphabet excluding vowels and Y s. Four hundred cards provided the set of test stimuli. The MS was a white card with a high density random array of letters and letter fragments. This visual noise masking stimulus is effective in interfering with further processing of the preceding TS in backward masking situations. The adaption field contained a card with a centered cross for use as a fixation point. Luminance in all fields was 15 footlamberts. Procedure The experimental procedure began with the subject fixating on the cross of the adapting field. When the subject was ready, the adapting field was replaced with a 15 msec presentation of the test stimulus, followed by a dark interval of variable duration (ISI), followed in turn by a 500 millisecond masking stimulus. Subjects responded to each trial by writing four letters on a specially prepared answer sheet. They were required to guess when unsure. Only those letters in the correct positions in the row were counted as correct. Six ISIs were employed: -1 5, 15, 30, 45, 60 and 75 msec plus a condition in which the TS was presented without MS. The -15 msec ISI condition, where both the TS and MS were presented simultaneously, was employed to demonstrate that MS did

3 Information Processing Rate 401 prevent the processing of the material in TS. These seven conditions were presented in blocks of 12 trials each. Subjects received one ascending and one descending series for a total of 168 trials. Half of the subjects received the ascending series first and half received stimuli in the reverse order. The first two trials of each block were warm-up trials and data were examined only for the last ten trials. Prior to any test sessions, subjects received two training sessions to minimize variability in performance. Subjects participated in three test sessions, one for each treatment, at one-week intervals. At each session subjects received a beverage containing either 0, or grams of alcohol per kilogram body weight in a beverage containing sufficient orange juice to produce a volume of one ounce per 12.5 pounds body weight. Two subjects were randomly assigned to each of the six possible treatment orders. Subjects were instructed not to eat for four hours preceding a test session. They were required to drink the beverage within 30 minutes; testing began 30 minutes after the subject finished drinking. The experimental task lasted approximately 30 minutes. RESULTS Mean scores of each treatment at each ISI are graphed in the Figure. Data were analyzed with a UCLA Biomedical Analysis of Variance Computing Program (1). In conformity with the literature on backward masking the results demonstrate that the length of time available for processing the visual information storage image (as set by the ISI length) determined the amount of information readout. Figure 1 indicates that alcohol produced a slowing of the rate at which information was read out of the sensory information storage. At all ISIs where the MS was presented and the response rate was above the guessing level, fewer letters were correctly reported under the alcohol treatments (F = 42.17, df = 2,10, p < 0.01). The mean curves presented in the Figure are characteristic of individual curves. Only one of the 12 subjects failed to show performance impairment under the lower alcohol dosage and all showed impairment under the higher alcohol dosage. OUl tr cr oo to cr UJ LU 4 r - A o = 0.0 g A L C /k g B O D Y W E IG H T (PLACEBO) = 0. 4 l 4 g A L C /k g B O D Y W E IG H T a = g A L C /k g B O D Y W E IG H T Figure 1 IN T E R -S T IM U L U S IN T E R V A L,(M IL L IS E C O N D S ) NO M A SK Mean scores o f three treatments at six inter-stimulus intervals.

4 402 H. Moskowitz and J. Murray The Figure suggests that the increment in performance as the ISI increased was roughly the same for all treatments. This was confirmed by a non-significant interaction term, Treatments X ISI, for all I Sis where performance was above guessing level, i.e., 30 to 75 msec (F = 2.51, df = 6, 6, not significant). The.414 g alcohol/kg bodyweight dose increased processing time about 5 to 7 msec and the.828 g alcohol/ kg bodyweight dose increased processing time about 15 to 20 msec. Thus the effect of the alcohol treatment appeared primarily upon the intercept of the curves rather than upon the slope. It should be noted that the alcohol treatments had no effect on information processing where ample time was permitted for processing, that is, in the condition where no mask was presented (F = 0.44, df = 2, 10, not significant). Thus in this experimental situation there was no impairment of sensory or motor performance, only of central processing. DISCUSSION The decreased number of correctly reported letters under the alcohol treatments supports the hypothesis that alcohol impairs the rate of information processing, at least for the function of reading information of the sensory storage image into STM. The degree of deficit found for alcohol upon information processing time reflects alcohol s influence only upon readout from the iconic image. It does not indicate an alcohol effect upon other links in the information processing chain. There well may be other information processing steps important for safe functioning in driving which are equally susceptible to the influence of alcohol. This experiment was one of a series which have been undertaken to determine the nature of alcohol impairment of skills performance. In several previous studies, it was found that performance requiring division of attention between two or more information inputs was uniquely sensitive to alcohol impairment at blood alcohol levels beginning at.015% (2,4,6,8,11). The results of this study suggest one possible mechanism underlying the sensitivity of divided attention performance to alcohol. This explanation is dependent on the assumption that while divided attention appears to be a parallel processing of information from diverse sources, microanalysis of the phenomenon suggests that it is a process involving serial processing of information sampled alternately from the various sources, except when information processing demands are very low. For such a serial sampling process to occur, a large capacity information storage buffer is required to hold the data from various channels while data is being processed more centrally from alternate channels. It is this function which the sensory information storage image is presumed to perform. Under these circumstances any delay in processing the information from one channel will result in a loss of information from the other channels which are being held in the short-lived sensory information storage. Thus a slowed rate of information processing will produce a decreased capacity to handle information from more than one channel if the quantity of information is beyond the capacity for parallel processing. However, even in situations where the amount of information to be processed does not require serial processing, the increase in processing time represents a danger in driving situations where a rapid response to threatening stimuli is required.

5 REFERENCES Information Processing Rate Dixon, W. J. (ed.), Biomedical Computer Programs. University of California Press, Los Angeles, California, Hamilton, P. and Copeman, A., The Effect of Alcohol and Noise on Components of a Tracking and Monitoring Task, British Journal o f Psychology 61, 149 (1970). 3. Keele, S. W., A ttention and Human Performance. Goodyear Publishing Co., Pacific Palisades, California, Moskowitz, H., Laboratory Studies of the Effects of Alcohol on Some Variables Related to Driving, Journal o f Safety Research 5, 185 (1973). 5. Moskowitz, H. and Burns, M. The Effect of Alcohol upon the Psychological Refractory Period, Quarterly Journal o f Studies on Alcohol 32, 782 (1971). 6. Moskowitz, H. and DePry, D. The Effect of Alcohol upon Auditory Vigilance and Divided Attention Task, Quarterly Journal o f Studies on Alcohol 29, 54 (1968). 7. Moskowitz, H. and Roth, S. The Effect of Alcohol upon the Latency in Naming Objects, Quarterly Journal o f Studies on Alcohol 32, 969 (1971). 8. Moskowitz, H. and Sharma, S. Effects of Alcohol on Peripheral Vision as a Function of Attention, Human Factors 16, 174 (1974). 9. Neisser, U., Cognitive Psychology. Appleton-Century-Crofts, New York, Sperling, G., The Information Available in Brief Visual Presentations, Psychological Monographs 74, 1 (1960). 11. Von Wright, J. M. and Mikkonen, V. The Influence of Alcohol on the Detection of Light Signals in Different Parts of the Visual Field, Scandinavian Journal o f Psychology 11, 167 (1970).

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