G. Robert Grice

Forest before trees? It depends where you look.

Because it may be deduced from the more elementary principles of visual processing, global precedence (Navon, 1977) is not a primary perceptual principle. Subjects were presented with a large letter made out of small ones and asked to make an identification response on the basis of either the large or small letter. When fixation was controlled to provide adequate stimulation from the small letter, there was no difference in reaction time (RT) between the large and small targets. Also, there was no difference in interference due to response incompatibility of the unattended letter based on target size. However, when the stimulus was presented peripherally, unpredictably to the right or left of fixation, RT was faster to the large target and interference was substantially greater for the small target. Functions for the development of associative strength and associative interference are presented. Global precedence is dependent on factors tending to degrade small stimuli more than large ones.

Temporal dynamics of associative interference and facilitation produced by visual context

Temporal dynamics of associative interference and facilitation have been investigated in a reaction time (RT) task in which a target letter is flanked by noise letters. When response-incompatible noise letters precede the target by stimulus onset asynchronies (SOAs) from 0 to 250 msec, associative interference, indicated by average RT, increases to a maximum at 50 and 100 msec and decreases substantially at 250 msec. Noise letters identical to the target do not produce facilitation with 0 SOA but do so when they precede the target by as little as 50 msec. Maximum facilitation is obtained with 100- and 250- msec SOAs. Temporal dynamics within the trial were inferred from scaling analyses of the RT distributions. The time course of associative interference is nonmonotonic, with the maximum occurring earlier as SOA increases. This confirms a prediction of continuous growth strength theory. Facilitation is primarily a short-latency effect, beginning earlier as SOA increases. At 0 SOA, there is evidence that an identical noise letter produces distraction as compared with a no-noise condition.

Absence of a redundant-signals effect in a reaction time task with divided attention.

In letter-identification reaction time experiments, a redundant-signals advantage was obtained when one location contained an irrelevant letter on single-target trials. It was not obtained when the position was blank. This confirms a prediction from a previous analysis in terms of variable criterion theory. The intercept of the linear function relating the growth of excitatory strength for redundant targets to that for the sum of single-target strengths is determined by the presence or absence of an irrelevant distractor. This confirms a second prediction. In this task, the redundant-signals advantage is due to distraction from an irrelevant stimulus occupying a relevant location. There is also evidence for a smaller distraction effect even from a redundant target. These findings are inconsistent with predictions of separate activation theory. Apparent differences be-tween these results and those of tachistoscopic recognition experiments are discussed.

Application of variable criterion theory to choice reaction time

A theory of choice reaction time ICRT is presented which is based on a variable criterion model assuming the decision criterion to be normally distributed. The theory provides functions of time describing the growth of component processes following stimulus onset. For correct responses, these processes are sensory and associative strength. For errors, the processes are sensory strength, generalized associative strength, and associative inhibition. A model for separating the effects of these processes from that of response competition is presented. The theory describes, with great accuracy, the CRT distributions of correct responses and errors, not only for the experiment for which it was derived, but also for a second experiment in which the criterion was experimentally manipulated. It accounts for the basic facts of the speed-accuracy tradeoff, not only with respect to the two experiments with different speed requirements, but also with respect to the variation of speed over trials within each experiment. While derived from group data, the theory also describes the performance of individual subjects. The mean and variability of the criterion distribution and the ability to utilize associative inhibition are identified as the major sources of individual differences. Methodological problems involved in the scaling analysis of group data are also discussed.

Application of a variable criterion model to auditory reaction time as a function of the type of catch trial

A variable criterion model has been applied to data from an RT experiment by LaBerge in which catch trial stimuli varied in similarity to a single auditory RT signal. Estimates of a sensory recruitment function and the parameters of hypothetical criterion distributions were obtained by a scaling solution. Auditory recruitment was an exponential growth function, and the criterion distributions were normal. In combination, these estimates successfully predicted the empirical RT distributions.

Temporal characteristics of noise conditions producing facilitation and interference

In reaction time (RT) experiments, a target letter was flanked by noise letters with differing relations to the target. When noise letters that are identical to the target, or response-compatible but not identical, precede the target by 100 msec, RT is facilitated. Facilitation by identical noise is greater. Scaling analysis of the RT distributions indicated that facilitation by compatible noise is a very short-latency, transient effect. Facilitation by identical noise is more persistent. It is suggested that there are two facilitative processes-direct response priming by compatibility, and facilitation of stimulus coding by stimulus identity. Facilitation is not obtained when these noise letters are presented simultaneously with the target. Associative interference is produced by response-incompatible noise letters, both with simultaneous presentation and with noise preceding the target. Maximum interference is earlier when noise precedes the target. This confirms previous findings and a prediction of continuous growth theory.

What makes targets redundant

Two letter-classification experiments that investigated target-redundancy effects on reaction time (RT) were conducted. Both experiments were replicated with choice reaction time (CRT) and go/no-go (GNG) procedures. In each experiment, there were two single-target conditions, one with a noise letter and one without. In one experiment, the letter classes were two letters that could be of either case. In the second experiment, each class consisted of two different capital letters. In both experiments, there were two redundant-targets conditions, one with identical targets and one with the different members of a class. In both of the GNG experiments, redundancy gains were obtained comparing the different-targets condition with the no-noise, single-target condition. Redundant stimuli are ones that lead to the same response. Visually different stimuli may be processed in parallel and jointly activate a response. GNG procedures are more sensitive than CRT in the investigation of redundancy effects.

Redundancy phenomena are affected by response requirements

Results are reported for two go/no-go reaction time (RT) experiments, in which the redundant targets advantage was investigated. These experiments were replications of two earlier choice reaction time (CRT) experiments, in which letter stimuli were used. Important differences between the go/no-go RT experiments and the CRT experiments were obtained. Equal and significant redundancy advantages were obtained whether redundant targets were compared with a single target presented with a noise letter or without noise. In the CRT experiments, the advantage was not obtained in the comparison with a single target presented alone. Noise letters did not slow the RTs to single targets with which they were presented as was the case with CRT. Since the differing results of the two procedures depend on the response requirements, explanation of differing CRT data in terms of perceptual or attentional concepts is probably inappropriate. The presence and absence of response competition in the two situations may be the best interpretation. The results tend to support a conclusion of the parallel processing of two letter stimuli separated spatially by as much as 3°.

Development of associative and perceptual interference

In a choice reaction-time letter-identification task, the temporal development of perceptual and associative interference was studied with visual displays containing identical, irrelevant, or response-incompatible noise letters. Using the methods of variable-criterion theory, it was determined that perceptual interference is complete very early and has no effect on the shape of the function for the growth of associative strength. Associative interference begins later, gradually increases to a maximum, and then declines to zero at long latencies. In experiments with speeded performance, it was also found that the growth of excitatory strength for errors contains the same nonmonotonic process as for correct responses, but in reverse form. In addition, it was observed that the discriminability of the target stimuli affects the rate of growth of associative strength for the correct response. Analyses of individual differences in theoretical parameters indicate information-processing patterns similar to those reported for simple auditory tasks.

Stimulus intensity, catch trial effects, and the speed-accuracy tradeoff in reaction time: A variable criterion theory interptation

Ss responded to a 1,000-Hz tone of 50, 80, or 100 dB. Catch trial conditions were none, blank trials, a red light, a noise, and an 1,800-Hz tone. Auditory catch signals were of the same intensities. RT distributions in the first three conditions were well described by a family of exponential growth functions dependent upon stimulus intensity and by the parameters of normal criterion distributions dependent upon catch trial conditions and between-session variability. Performance in the auditory catch trial conditions was not dependent upon the same set of sensory growth functions. Performance in these conditions was described by a two-dimensional analysis of information transmitted as a function of time and interpreted in terms of variable criterion theory. The speed-accuracy tradeoff in this situation appears to depend upon differential rates of growth of intensity and associative information and the criterion used in responding to this information.