An "exhaustive" search for tasks that fall between the choice and simple reactions.

An experimental search was made for reaction time (RT) tasks that require the processing operation of stimulus discrimination or response selection, but not both. The existence of such a task would allow the subtractive determination of the mean duration of the separate operations. Each of the three reactions that historically have been represented as possessing only one of the two operations was subjected to empirical testing. None of them met the most basic requirements. Donders' (1868/1969) contingent (c) reaction and Taylor's (1966) selection (b')reaction were not reliably faster than a compatible choice (b) reaction. Wundt's (1880) discrimination (d) reaction was not sensitive to difficulty of discrimination. The possibility is suggested that stimulus discrimination and response selection in the choice reaction are inseparable operations. The present negative results emphasize the importance of establishing validity of any use of the subtraction method through appropriate experimental methods. Some parallels of the compatibility issue are found in experiments in which RT is used as a measure of the duration of programming operations.

Generalizations and extensions of the precue-utilization effect in rapid reactions.

The method of brief PSIs (precue-to-stimulus intervals) was used in three RT (reaction-time) experiments to explore the generality of the precue-utilization effect in rapid reactions, and to examine two extensions. This effect, which shows the self-contained performance in the choice reaction of the processing operations that culminate in response selection, generalized to a quantitative discrimination and to unequal stimulus-response (SR) frequencies. In the first extension, the reduction in wrong-alternative errors at relatively long PSIs indicated that these errors occur in conjunction with commitment to response actualization. In the second extension, the duration of discrimination-selection was found to be no longer for the less frequent of two SR alternatives. Taken together, these findings indicate that the effect of relative SR frequency, on incidence of errors as well as length of RT, fell on response-actualization processing. This is in accord with a number of previous findings and consonant with effects of RT variables on movement parameters but contrary to cumulative speed-accuracy models.

Verification of Donders' subtraction method.

In an experiment on 6 young adults advance (precued) information of the correct choice response was utilized completely: (a) For precue-to-stimulus intervals (PSIs) clearly shorter than the difference between mean choice and simple reaction time (RT), median response latency (L) measured from precue onset was invariant; (b) For clearly longer PSIs, median RT was very near the value for simple RT. This precue-utilization effect would be expected if response actualization had been delayed until the response had been selected and if the requirement for discrimination and selection had no adverse effect on readiness to respond. Donders' (1868/1969) hypothesis in his initial application of the subtraction method, that choice and simple reactions are identical except for the serial insertion of discrimination and selection operations in the former, is thereby strongly supported. If this formulation is accepted, models that hold that response processing can overlap other processing stages may be considered valid only for response selection, not response actualization.

Effort of preparation and age.

In an experiment on 24 men and women who were selected for short simple RT (reaction time) and who ranged from 22 to 86 yr. of age, choice RT increased monotonically over 3.5 sec. of waiting time during which there was high momentary probability of stimulus occurrence. As use of a choice reaction minimized the possibility of a response set, the occurrence of a waiting decrement was regarded as support for Näätänen's 1971 proposal of short-term mental exhaustion, which was derived from a similar study but for simple RT. The effect of age on endurance was not clear. There appeared to be no greater waiting decrement with age up to about 65 yr., but the possibility of greater decrements beyond that age cannot be discounted. The existence of short-term exhaustion is consonant with Kahneman's (1973) view that effort is required for the generation of processing capacity. Kahneman and other investigators of mental effort have unanimously rejected the existence of any appreciable effort during preparation. However, Näätänen's evidence for short-term exhaustion apparently had not been considered. It is here suggested that short-term exhaustion usually is not incurred in information processing tasks as they are characterized by alternations of high and low demands for capacity, unlike the present high constant momentary probability of signal occurrence. It is further conjectured that such intermittent operation evolved as the optimum way of utilizing underlying resources that are subject to depletion.

Age and simple reaction time.

Although simple reaction time (RT) to a tone showed a statistically significant increase between 18 and 93 years of age in a sample of 220 men and women, the amount of increase was slight, less than 2 msec/decade. Consequently, the appreciable slowing of more typical behavior with age does not seen attributable to some general process in the central nervous system as has been argued. This degree of stability found for simple RT with age, unexpected from the body of previous work, may reflect equivalence of age groups and use of optimal RT technique. In a second study eight old participants (73 to 84 years) matched on the optimal technique with eight young participants (18 to 24 years) were markedly slower with a long constant preparatory interval but not with elimination of timing cues. Together, the two studies show that simple high level of preparation was either easy of impossible to attain. Behavioral slowing with age can result from ineffective control processes.

Aging and the use of advance probability information.

Two experiments were performed to investigate the relation between age and use of advance probability information to prepare for a simple response. In both, an occasional presignal occurring about.5 sec before a possible response signal informed the subject that the probability of a response signal had increased from.1 to.5 In experiment 1, 24 women and men selected for short RT were tested, all between 21 and 78 yr of age. Subjects under 50 were able to use the advance information to shorten their RTs as were the majority of older subjects. However, for some older subjects the presignal produced a negative effect, a paradoxical lengthening of RT. In Experiment 2, using five of the older subjects from Experiment 1, more intensive testing was done with closer spacing of trials. Subjects who previously showed a lengthening of RT with the presignal now showed the typical shortening. In summary, over the age span investigated, almost all selected older subjects as well as younger subjects.

Aging and the maintaining of preparation.

In an experiment on 25 women and men who were selected for short RT (reaction time) and who ranged from 22 to 85 years of age, some loss of preparation was found over an interval of about 4 seconds during which there was constant momentary probability of signal occurrence. The central finding was that the amount of loss remained invariant with age. Numerous controls were used to ascertain that this stability was not an artifact. Support was given to the contention of Loveless and Sanford [14] that the markedly longer RTs found for older than for younger subjects when long, constant PIs (preparatory intervals) are employed is not attributable to difference in ability to maintain preparation. However, the reason for the foregoing effect remains in question. Loveless and Sanford [14] suggest that older subjects may not be able to control preparation in some more general sense and suggest that they do not use available timing information. However, similar findings on schizophrenics have been explained in terms of inhibitory effects with increased redundancy [1]. A method is suggested for eliminating the artifactual shortening of RT at the longest waiting period found in studies using the present method for measuring the maintaining of preparation.

Reaction time and probability on isolated terms.

The reaction-time probability effect on isolated trials was found to be asymmetrical in an experiment on 64 college students. There was a large drop in RT for a high-probability probe trial embedded in a block of low-probability trials, but a much smaller rise for a low-probability trial embedded in high-probability trials. Thus, low- but not high-probability responses seem to be influenced by characteristics of the trial block. If the basis of the probability effect were the strategic placement of the criterion for response initiation, symmetrical results should have been obtained. A motivational account which accords with the present data is that the subject is ordinarily willing to prepare but is averse to doing so in some (not entirely specified) low-probability circumstances.

The persistence of psychological refractoriness.

The view that psychological refractoriness is a fundamental characteristic of human performance was supported by its survival of a determined attempt to eliminate it through training. An S was given practice for 87 days on a successive choice-response task with a constant inter-signal interval of 100 msec. Although his performance became better than any exhibited by Ss with more typical practice, he was not able to reduce psychological refractoriness to less than 20 or 25 msec. Moreover, when S was then shifted to variable inter-signal intervals he showed greater than the usual amount of psychological refractoriness at the intervals next longer than 100 msec. This indicated that he had learned a special skill rather than a generally "less refractory" mode of response (or merely better technique on the separate tasks). Training was found to be an effective way of eliminating holding back on the first response.

Uncertainty, timekeeping, and simple reaction time.

Implications of the hypothesis that effects on simple RT of event and time uncertainty are due to S's unwillingness to prepare for an unlikely event were tested. In 2 experiments, RT was compared for the foreperiod method and the new transit-signal method. Alternative hypotheses based on faulty reinstatement of foreperiods were invalidated. The inverse relation of RT to event uncertainty persisted for the transit-signal method which is free of memory effects. With time uncertainty the initial gradient of RT was steeper with the transit-signal method. There S had before him exact time information for estimating momentary probability of a signal. The uncertainty effect occurred even though it was evident that S could overcome it, so the term unwillingness is appropriate. Consequences of inaccurate timekeeping were examined; the contention that it simply and invariably increases RT was not supported. Unwillingness was examined in terms of the utility associated with preparation.