Random number generation and the frontal cortex

The Effects of Total Sleep Deprivation on the Generation of Random Sequences of Key-Presses, Numbers and Nouns

According to a recent hypothesis, executive functions should be particularly vulnerable to the effects of total sleep deprivation. Random generation is a task that taps executive functions. In three experiments we examined the effects of total sleep deprivation on random generation of keypresses, numbers, and nouns, in particular on the suppression of prepotent responses and the selection of next responses by way of applying a local-representativeness heuristic. With random key-presses suppression of prepotent responses did not suffer from lack of sleep, but it became poorer at a sufficiently high pacing rate. In contrast, suppression of prepotent responses suffered when numbers and nouns were generated. According to these findings different types of random generation tasks involve different types of inhibitory process. With only four response alternatives, but not with larger response sets, application of the local-representativeness heuristic was impaired after a night without sleep. In terms of a simple formal model, serial-order representations of the preceding responses are used in selecting the next response only for the small response set, and not for larger response sets. Thus, serial-order representations are likely to suffer from loss of sleep. These findings strongly suggest that random generation involves multiple processes and that total sleep deprivation does not impair all sorts of executive functions, but only some.

Assessing executive functioning: on the validity, reliability, and sensitivity of a click/point random number generation task in healthy adults and patients with cognitive decline

In random number generation (RNG) tasks, used to assess executive functioning, participants are asked to generate a random sequence of digits at a paced rate, either verbally or by writing. Some previous studies used an alternative format in which participants had to randomly press different response keys, assuming that this task version demands the same cognitive processes as those implied in the standard version. The present study examined the validity of this assumption. To this end, the construct validity, reliability, and sensitivity of a conceptually similar task version of the key-press task were examined. Participants had to randomly click on, or point to, the digits 1-9, laid out orderly in a 3 × 3 grid on a computer screen. Psychometric properties of this task were examined, based on the performance of 131 healthy participants and 80 patients with cognitive decline. The results suggest that the click/point RNG task version can be used as a reliable and valid substitute for standard task versions that use the same response set and response pacing rate as those used in the present study. This task might be a useful alternative, demanding no separate recording and recoding of responses, and being suitable for use with patients with speech or writing problems.

Random noun generation in younger and older adults

We examined age-related changes of executive functions by means of random noun generation. Consistent with previous observations on random letter generation, older participants produced more prepotent responses than younger ones. In the case of random noun generation, prepotent responses are nouns of the same category as the preceding noun. In contrast to previous observations, older participants exhibited stronger repetition avoidance and a stronger tendency toward local evenness—that is, toward equal frequencies of the alternative responses even in short subsequences. These data suggest that at higher adult age inhibition of prepotent responses is impaired. In addition, strategic attentional processes of response selection are strengthened, in particular the application of a heuristic for randomness. In this sense response selection is more controlled in older than in younger adults.

Random number generation during sleep deprivation: effects of caffeine on response maintenance and stereotypy

Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. Previous neuropsychological studies indicate that sleep deprivation causes impairments in prefrontal cortical function. Random number generation (RNG) is thought to provide a sensitive index of executive functions that rely on the prefrontal cortex. The present study tested the hypothesis that sleep deprivation would impair RNG and that caffeine would mitigate this impairment. Healthy young men (n = 21) participated in two 40-h sleep deprivations 1 week apart. During each sleep deprivation period subjects received either caffeine or placebo according to a randomized, double-blind cross-over design, and they completed an oral RNG task at 3-h intervals. Comparison of test sessions at analogous times of day revealed that sleep deprivation was associated with significant drops in the number of responses, a threefold increase in the percentage of rule violations, 59% greater response redundancy and a 20% increase in stereotypy of adjacent response pairs. Sleep deprivation did not consistently alter counting tendency. Caffeine ameliorated the decrease in the number of responses but did not mitigate other deficits in RNG that arose during sleep deprivation. These findings are consistent with prior reports of diminished vigilance and increased perseveration during extended wakefulness. They support the conclusion that caffeine preserves simple aspects of cognitive performance during sleep deprivation, whereas caffeine may not prevent detrimental effects of sleep deprivation on some complex cognitive functions.

Performance of university students on random number generation at different rates to evaluate executive functions

OBJECTIVE: To evaluate the performance of adult young subjects in a Random Number Generation (RNG) task by controlling the response speed (RS). METHOD: Sixty-nine university students of both sexes took part in the experiment (25.05 ± 6.71 year-old). Participants were alloted into 3 groups which differed in RS rates to generate numbers: 1, 2 and 4 seconds to generate each number. A digital metronomer was used to control RS. Participants were asked to generate 100 numbers. The responses were mensured through Evans's RNG Index. RESULTS: There were statistically significant differences among the groups [F (3, 68) = 7.120; p < .05]. Differences were localized between 1 and 2 seconds (p = 0.004) and between 1 and 4 seconds (p = 0.006). No differences were observed between 2 and 4 seconds (p = 0.985). CONCLUSION: The present results suggest that the response speed in production of random numbers influences the performance of the Random Numbers Generation task.

Variables that influence the generation of random sequences: an update

This article updates Tune's 1964 review of variables influencing human subjects' attempts at generating random sequences of alternatives. It also covers aspects not included in the original review such as randomization behavior by patients with neurological and psychiatric disorders. Relevant work from animal research (spontaneous alternation paradigm) is considered as well. It is conjectured that Tune's explanation of sequential nonrandomness in terms of a limited capacity of short-term memory can no longer be maintained. Rather, interdependence among consecutive choices is considered a consequence of an organism's natural susceptibility to interference. Random generation is thus a complex action which demands complete suppression of any rule-governed behavior. It possibly relies on functions of the frontal lobes but cannot otherwise be "localized" to restricted regions of the brain. Possible developments in the field are briefly discussed, both with respect to basic experiments regarding the nature of behavioral nonrandomness and to potential applications of random-generation tasks.

Random number generation in dementia of the Alzheimer type: a test of frontal executive functions

The quality of attempts at generating a random sequence of the numbers 1-6 was studied in 30 patients with dementia of the Alzheimer type (DAT) and 30 elderly normal control (NC) subjects. Three main findings emerged: (1) DAT patients' subjective random sequences were more streotyped (contained fewer digit combinations) than those of NC subjects. (2) This difference in response stereotypy was due to patients' enhanced tendency to arrange consecutive numbers in an ascending series ('counting bias'). (3) In the patient group, degree of sequential nonrandomness was positively correlated with overall severity of dementia and with the extent to which performance on neuropsychological tests specifically assessing executive functions (fluency, naming, error monitoring) was impaired. These results illustrate a loss of behavioral complexity in the course of dementia and are interpreted as reflecting a frontal dysexecutive syndrome in DAT.