After-effects of responding and of withholding responses in C.RT tasks

The effects of response repetition on choice RT were compared in b-reaction and in c-reaction tasks [Experiments I(a) and I(b)]. The difference in RTs for repeated and for non-repeated responses was found to be less for c-reaction than for b-reaction tasks. This seemed to be because in c-reaction tasks subjects can prepare themselves to make the same response on every trial, so that there is little further RT reduction consequent on immediate response repetition. In b-reaction tasks subjects cannot always prepare to make the same response, so that the difference between response repetition RT and responce alteration RT is greater. Experiment II examined transitions between events in a serial, self-paced C.RT task in which subjects made a different response to each of two signals but withheld any response to the onset of a third. In this task responses were faster when they followed other, different responses than when they followed “no go” trials. The results of these experiments allow us to reject, even for very elementary tasks, a simple “S--R connection network” model for the processes involved in the identification of signals and the production of responses to them.     

Actively Controlling Anticipation of Irregular Events

There have been no investigations as to how people respond to sequences of events which occur at brief, unpredictable intervals as in everyday life. Eleven young adults were practised at a two-choice, continuous, serial choice-response task in which intervals between each response and the onset of the next signal (RSIs) varied randomly from trial to trial. On half the trials in each of four conditions the RSI was 20 ms, and on the other trials 200, 400, 800 and 1600 ms respectively. Reaction times fell as RSIs increased from 20-200 ms but thereafter appeared to be unaffected by RSI duration. In the 20/200 and 20/400 ms RSI conditions RT was not affected by transitions between different RSIs but in the 20/800 and 20/1600 ms conditions RTs were faster when the longer RSI recurred on immediately successive trials than if the long RSI followed the short (20 ms) RSI. These results are discussed in terms of a control system model for the way in which subjects actively trade off between their internal performance limitations to optimally meet task demands.     

Modulation of selective attention by sequential effects in visual search tasks

In visual search detection of a target on one display facilitates its subsequent recognition on the next (Rabbitt, Cumming and Vyas, 1977). Experiment I shows that facilitation also occurs when a different display intervenes between two displays containing targets. Two further experiments show that detection of target letters among background letters is also facilitated if the same background letters recur on successive displays. Facilitation is greatest if background letters reappear in identical left-to-right spatial locations, but is also evident when the same background letters recur in different locations on successive displays. The results suggest modifications to models for the ways in which selective attention is continuously modulated by successive events during serial search.     

Processing a display even after you make a response to it. How perceptual errors can be corrected

We know that when people make responses which they did not intend they can discover this by monitoring kinaesthetic and visual feedback. It is less clear whether they can also correct perceptual errors which occur when they mistake one signal for another. It was argued that, if they can sometimes do this, extra errors which occur when discriminations become more difficult may be detected and corrected. Experiment I compared the ability of young fit subjects to detect errors made during easy and during difficult discriminations between tone signals. There was no evidence that any additional errors made to difficult discriminations were detected. Fast errors were detected, slower errors were not. The results were consistent with the idea that subjects can detect fast motor errors by monitoring feedback, but that they cannot detect perceptual mistakes.

In Experiment II subjects made easy and difficult line length discriminations. Displays lasted for 100 ms, 200 ms or 500 ms and were followed by random masks. In this case, fast errors were again corrected more frequently than slow errors but eight aspects of the data suggest that subjects could, and did, correct perceptual as well as motor mistakes and that they managed to do this by continuing to process a display after the moment at which they may have initiated an impulsive response to it. The data are interpreted in terms of a “Committee Decision” model for extended perceptual processing previously applied to other, similar data by Rabbitt and Rodgers (1977) and Rabbitt, Cumming and Vyas (1978).     

An evolutionary approach to support decision making with linear decision models

In this paper we consider decision problems that can be described as linear decision models. These models have been traditionally solved using linear programming, fuzzy linear programming, multiple-objective linear programming or ‘what-if’ analysis. Using these approaches, one encounters a number of difficulties. We propose an ‘evolutionary approach’ to overcome these difficulties. In the proposed approach the decision maker does not have to precisely specify the model (i.e. the objective functions, the RHS values, etc.) at the beginning of the solution procedure. In fact, the model evolves as the solution procedure proceeds.