Connectionist and diffusion models of reaction time.

Two connectionist frameworks, GRAIN (J. L. McClelland, 1993) and brain-state-in-a-box (J. A. Anderson, 1991), and R. Ratcliff's (1978) diffusion model were evaluated using data from a signal detection task. Dependent variables included response probabilities, reaction times (RTs) for correct and error responses, and shapes of RT distributions. The diffusion model accounted for all aspects of the data, including error RTs that had previously been a problem for all response-time models. The connectionist models accounted for many aspects of the data adequately, but each failed to a greater or lesser degree in important ways except for one model that was similar to the diffusion model. The findings advance the development of the diffusion model and show that the long tradition of RT research and theory is a fertile domain for development and testing of connectionist assumptions about how decisions are generated over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling aging effects on two-choice tasks: Response signal and response time data.

In the response signal paradigm, a test stimulus is presented, and then at one of a number of experimenter-determined times, a signal to respond is presented. Response signal, standard response time (RT), and accuracy data were collected from 19 college-age and 19 60- to 75-year-old participants in a numerosity discrimination task. The data were fit with 2 versions of the diffusion model. Response signal data were modeled by assuming a mixture of processes, those that have terminated before the signal and those that have not terminated; in the latter case, decisions are based on either partial information or guessing. The effects of aging on performance in the regular RT task were explained the same way in the models, with a 70- to 100-ms increase in the nondecision component of processing, more conservative decision criteria, and more variability across trials in drift and the nondecision component of processing, but little difference in drift rate (evidence). In the response signal task, the primary reason for a slower rise in the response signal functions for older participants was variability in the nondecision component of processing. Overall, the results were consistent with earlier fits of the diffusion model to the standard RT task for college-age participants and to the data from aging studies using this task in the standard RT procedure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A random-walk model of accuracy and reaction time applied to three experiments on pigeon visual discrimination.

A random-walk model of visual discrimination is described and applied to reaction time (RT) distributions from three discrete-trial experiments with pigeons. Experiment 1 was a two-choice hue discrimination task with multiple hues. Choice percentages changed with hue discriminability; RTs were shortest for the least and most discriminable stimuli. Experiments 2 and 3 used go/no-go hue discriminations. Blocks of sessions differed in reward probability associated with a variable red stimulus in Experiment 2 and with a constant green stimulus in Experiment 3. Changes in hue had a large effect on response percentage and a small effect on RT; changes in reward shifted RT distributions on the time axis. The “random-walk, pigeon” model applied to these data is closely related to Ratcliff's diffusion model (Ratcliff, 1978; Ratcliff & Rouder, 1998). Simulations showed that stimulus discriminability affected the speed with which evidence accumulated toward a response threshold, in line with comparable effects in human subjects. Reward probability affected bias, modeled as the amount of evidence needed to reach one threshold rather than the other. The effects of reward probability are novel, and their isolation from stimulus effects within the decision process can guide development of a broader model of discrimination. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A Diffusion Model Analysis of the Effects of Aging in the Lexical-Decision Task.

The effects of aging on response time (RT) are examined in 2 lexical-decision experiments with young and older subjects (age 60-75). The results show that the older subjects were slower than the young subjects, but more accurate. R. Ratcliff s (1978) diffusion model provided a good account of RTs, their distributions, and response accuracy. The fits show an 80-100-ms slowing of the nondecision components of RT for older subjects relative to young subjects and more conservative decision criterion settings for older subjects than for young subjects. The rates of accumulation of evidence were not significantly different for older compared with young subjects (less than 2% and 5% higher for older subjects relative to young subjects in the 2 experiments). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of aging and IQ on item and associative memory.

The effects of aging and IQ on performance were examined in 4 memory tasks: item recognition, associative recognition, cued recall, and free recall. For item and associative recognition, accuracy and the response time (RT) distributions for correct and error responses were explained by Ratcliff's (1978) diffusion model at the level of individual participants. The values of the components of processing identified by the model for the recognition tasks, as well as accuracy for cued and free recall, were compared across levels of IQ (ranging from 85 to 140) and age (college age, 60–74 years old, and 75–90 years old). IQ had large effects on drift rate in recognition and recall performance, except for the oldest participants with some measures near floor. Drift rates in the recognition tasks, accuracy in recall, and IQ all correlated strongly. However, there was a small decline in drift rates for item recognition and a large decline for associative recognition and cued recall accuracy (70%). In contrast, there were large effects of age on boundary separation and nondecision time (which correlated across tasks) but small effects of IQ. The implications of these results for single- and dual-process models of item recognition are discussed, and it is concluded that models that deal with both RTs and accuracy are subject to many more constraints than are models that deal with only one of these measures. Overall, the results of the study show a complicated but interpretable pattern of interactions that present important targets for modeling. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Concussion does not impact intraindividual response time variability.

This investigation examined the effect of concussion on intraindividual variability in 5 processing speed tasks. Forty-four adults, including 22 concussed and 22 healthy age- and gender-matched participants, completed the Headminder Concussion Resolution Index (D. M. Erlanger, D. J. Feldman, K. C. Kutner,& M. McCrea, 2001) twice. The test consists of a series of tasks including 25 trials of simple response time task, 70 trials of cued response time task (CuRT), 60 trials each for 2 visual recognition tasks, and 30 trials of symbol scanning task. Concussed participants completed a preinjury baseline assessment and were retested within 48 hours of injury diagnosis. The nonconcussed participants were retested 45 days after initial assessment. Average response time (RT), standard deviation, and response accuracy were calculated for each individual. Overall, concussed individuals had increased RTs across all tasks and were less accurate in the CuRT. RT variability for all tasks was elevated in concussed individuals, but controlling for mean RT at follow-up eliminated group differences. These findings indicate that response-time-variability increases in concussed individuals are proportional to processing-time increases. As such, RT variability is not a unique identifier of cognitive dysfunction following concussion. These results highlight that transient brain injury has significantly different neurobiological consequences than chronic conditions have. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of priming, discriminability, and reinforcement on reaction-time components of pigeon visual search.

Pigeons searched computer screens for 1 of 4 letter targets among 55 alphanumeric distractors. In Experiment 1, valid-cue trials used distinctive patterns to signal the subsequent appearance of specific targets, whereas ambiguous-cue trials used a signal common to all targets. Search reaction times (RTs) after valid cues were shorter than after the ambiguous cue; increased target discriminability also reduced RT. In Experiment 2, when reinforcement for 2 targets shifted from 10% to 20%, RTs to those targets dropped, whereas RTs to the other 2 targets rose. RT distributions suggested that precues and discriminability both affect the momentary probability of finding a target, as embodied in the decay constant of an underlying exponentially distributed RT component. Reinforcement changes appeared to affect different components of the response process, embodied in changes in the mean of an underlying lognormal distribution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hierarchical diffusion models for two-choice response times.

Two-choice response times are a common type of data, and much research has been devoted to the development of process models for such data. However, the practical application of these models is notoriously complicated, and flexible methods are largely nonexistent. We combine a popular model for choice response times—the Wiener diffusion process—with techniques from psychometrics in order to construct a hierarchical diffusion model. Chief among these techniques is the application of random effects, with which we allow for unexplained variability among participants, items, or other experimental units. These techniques lead to a modeling framework that is highly flexible and easy to work with. Among the many novel models this statistical framework provides are a multilevel diffusion model, regression diffusion models, and a large family of explanatory diffusion models. We provide examples and the necessary computer code. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Timing and reaction time.

Because reaction time (RT) tasks are generally repetitive and temporally regular, participants may use timing strategies that affect response speed and accuracy. This hypothesis was tested in 3 serial choice RT experiments in which participants were presented with stimuli that sometimes arrived earlier or later than normal. RTs increased and errors decreased when stimuli came earlier than normal, and RTs decreased and errors increased when stimuli came later than normal. The results were consistent with an elaboration of R. Ratcliff's diffusion model (R. Ratcliff, 1978; R. Ratcliff & J. N. Rouder, 1998; R. Ratcliff, T. Van Zandt, & G. McKoon, 1999), supplemented by a hypothesis developed by D. Laming (1979a, l979b), according to which participants initiate stimulus sampling before the onset of the stimulus at a time governed by an internal timekeeper. The success of this model suggests that timing is used in the service of decision making. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Continuous versus discrete information processing: Modeling accumulation of partial information.

Comments on D. E. Meyer and colleagues' (see record 1988-28535-001) new technique for examining the time course of information processing, which is a variant of the response signal procedure: On some trials Ss are presented with a signal that requires them to respond, whereas on other trials they respond normally. The accuracy of guesses based on partial information can be determined by using the data from the regular trials and a simple race model to remove the contribution of fast-finishing regular trials from signal trial data. This analysis shows that the accuracy of guesses is relatively low and is either approximately constant or grows slowly over the time course of retrieval. Myers et al argue that this pattern of results rules out most continuous models of information processing. But the analyses presented in the present article show that this pattern is consistent with several stochastic RT models: the simple random walk, the runs, and the continuous diffusion models. The diffusion model is assessed with data from a new experiment using the study–test recognition memory procedure. Fitting the diffusion model to the data from regular trials fixes all parameters of the model except one (the signal encoding and decision parameter). With this one free parameter, the model predicts the observed guessing accuracy. It is concluded that the results obtained from Meyer and colleagues' new technique give qualitative support to some stochastic models and quantitative support to the continuous diffusion model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortical and subcortical visual evoked potential correlates of reaction time in monkeys.

Investigated the relationships between reaction time (RT) and evoked potentials in 3 monkeys ( Macaca nemestrina ) during the performance of a simultaneous brightness discrimination task. Evoked potentials from the lateral geniculate, medial and inferior pulvinar, midbrain reticular formation, hippocampus, and striate and prestriate cortex were recorded concurrently with RT in response to the discriminative stimuli. An early component of the geniculate response and a late positive wave in striate cortex were found to be related systematically to RT. These components were largest for short RTs and diminished progressively in amplitude as RT lengthened. The statistical significance of these relationships is supported by a detailed analysis of single trials. The increases in amplitude of evoked potentials associated with short RTs are attributed to increased arousal level and are discussed in terms of reticular formation modulation of central excitability levels. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What are the shapes of response time distributions in visual search?

Many visual search experiments measure response time (RT) as their primary dependent variable. Analyses typically focus on mean (or median) RT. However, given enough data, the RT distribution can be a rich source of information. For this paper, we collected about 500 trials per cell per observer for both target-present and target-absent displays in each of three classic search tasks: feature search, with the target defined by color; conjunction search, with the target defined by both color and orientation; and spatial configuration search for a 2 among distractor 5s. This large data set allows us to characterize the RT distributions in detail. We present the raw RT distributions and fit several psychologically motivated functions (ex-Gaussian, ex-Wald, Gamma, and Weibull) to the data. We analyze and interpret parameter trends from these four functions within the context of theories of visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response bias, criteria settings, and the fast-same phenomenon: A reply to Ratcliff.

R. Ratcliff (see record 1985-19264-001) simulated data from 3 letter-matching experiments with his diffusion model. The fits were accomplished by varying 3 criteria, an encoding (or comparison) criterion and same and different response criteria. It is suggested that the necessity of including a comparison criterion is consistent with the conclusion of the present author and colleagues (see record 1985-11336-001) that bias of response criteria, alone, is insufficient to generate the fast-same phenomenon (faster same than different responses, often accompanied by a predominance of false-different errors). Although the diffusion model generates the commonly obtained pattern of reaction times (RTs) and errors through the settings of criteria, it does so by postulating complex patterns of settings, with no theoretical rationale for why or when they occur. The specific fits of the model violate several widely accepted psychophysical principles. It is concluded that criteria setting cannot be regarded as an adequate account of the fast-same phenomenon unless a psychologically meaningful rationale is developed for predicting the situations in which particular settings of criteria will be adopted. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recalibrating the auditory system: A speed-accuracy analysis of intensity perception.

Recalibration in loudness perception refers to an adaptation-like change in relative responsiveness to auditory signals of different sound frequencies. Listening to relatively weak tones at one frequency and stronger tones at another makes the latter appear softer. The authors showed recalibration not only in magnitude estimates of loudness but also in simple response times (RTs) and choice RTs. RTs depend on sound intensity and may serve as surrogates for loudness. Most important, the speeded classification paradigm also provided measures of errors. RTs and errors can serve jointly to distinguish changes in sensitivity from changes in response criterion. The changes in choice RT under different recalibrating conditions were not accompanied by changes in error rates predicted by the speed-accuracy trade-off. These results lend support to the hypothesis that loudness recalibration does not result from shifting decisional criteria but instead reflects a change in the underlying representation of auditory intensity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Speeded old-new recognition of multidimensional perceptual stimuli: Modeling performance at the individual-participant and individual-item levels.

Observers made speeded old-new recognition judgments of color stimuli embedded in a multidimensional similarity space. The paradigm used multiple lists but with the underlying similarity structures repeated across lists, to allow for quantitative modeling of the data at the individual-participant and individual-item levels. Correct-rejection response times (RTs) got systematically faster as the similarity of foils to the old study items decreased. There were also intricate patterns of speed-accuracy trade-offs that varied across individual items and participants. An exemplar-based random-walk model provided a good overall quantitative account of the recognition choice probabilities, mean correct RTs, and mean error RTs associated with the individual items on the basis of their positions in multidimensional similarity space. However, the model failed to predict the very long RTs associated with correct rejections of a prototype foil. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mental rotation interferes with response preparation.

Reaction times (RTs) and lateralized readiness potentials (LRPs) were studied to find out whether response preparation begins after mental rotation finishes, as assumed by discrete-stage models. Stimuli were disoriented normal or mirror-image characters, with character name determining which hand would respond. In Experiment 1, the normal/mirror-image information determined whether the response was to be executed (go) or withheld (no-go), and LRPs indicated that responses were weakly prepared before the end of mental rotation. Mental rotation was not required in Experiment 2, and significantly more response preparation was observed. In Experiment 3, probe RT trials embedded in the mental rotation task indicated that hand information is available to the response preparation process during rotation. Apparently, some response preparation occurs before mental rotation finishes, but rotation interferes with response preparation. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Psychophysically principled models of visual simple reaction time.

Visual psychophysics has shown that the perceptual representation of a stimulus has complex time-varying properties that depend on the response characteristics of the channel on which it is encoded. A fundamental expression of these properties is the distinction between sustained and transient processing channels. A theoretical and mathematical framework is introduced that allows such properties to be incorporated into fully stochastic models of simple reaction time (RT). These models, the multichannel leaky stochastic integrators, combine a linear filter model of stimulus encoding with an accumulative decision process and yield a stimulus representation described by a time-inhomogeneous Ornstein-Uhlenbeck diffusion process. Methods for obtaining RT distributions for these models are described, together with comparative fits to luminance-increment data obtained under conditions of channel pooling and channel independence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stability of visual expectations at 3.0 months of age.

Three-month-old infants were observed on 2 days to examine stability in forming visual expectations. Babies saw pictures that appeared in left–right alternation, 700-ms on with a 1,000-ms ISI. Anticipatory fixations and speeded reaction times (RTs) were the indexes of expectation. Split-half correlations were stable for each session (r?=?>.42, for RTs, and r?=?>.51, for % anticipations). The Session-1–Session-2 correlation was stable for median RTs (r?>?.48) and marginal for % anticipations (r?=?.34). The Session-1–Session-2 correlation for optimal RT (fastest median RT in a block of 10 trials) was r?=?.67. This correlation remained stable (r?=?.61) when the median RT for the first 10 pictures was partialed out. Thus, the optimal RT correlation reflected the effect of expectations on RT, apart from natural quickness. Eye-movement RT is a reliable performance measure in 3-month-olds, and individual differences exist in infants' tendency to form visual expectations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Theoretical interpretations of the speed and accuracy of positive and negative responses.

Examines different interpretations of the RT difference between positive and negative responses in 2-choice matching tasks. R. W. Proctor and colleagues (see PA, Vols 66:4888; 69:11757 and 11886; 71:11296; and 72:11336) hold that the difference represents a difference in processing between same and different judgments, whereas the author and M. J. Hacker (see PA, Vols 67:8976 and 69:11758) argue that the difference can be accounted for in terms of criteria settings. The ways in which several models (including sequential sampling models and mixture models) of choice RT and matching can account for this RT difference are examined, and one particular model, the author's diffusion model (see record 1982-02760-001), is fitted to data from 3 experiments. Results of these fits provide a clear interpretation of the RT difference in terms of criteria settings. It is concluded that interpretation of such positive–negative RT differences in the absence of a specific model is hazardous at best. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motor coactivation revealed by response force in divided and focused attention.

Four experiments examined effects of bimodal stimulation on response force (RF) in addition to reaction time (RT). In a divided-attention task (Exps 1–3), Ss were asked for a speeded response to either a visual or an auditory signal. In unimodal signal trials, either a visual or auditory signal was presented alone, and in redundant-signals trials, both signals were presented simultaneously. The same stimulus arrangement was used in a focused-attention task (Exp 4), but Ss had to withhold their response when an auditory signal was presented alone. In all experiments, the fastest RTs were attained in redundant-signals trials. In addition, RF was largest in redundant-signals trials, especially in the divided-attention task, suggesting a motor coactivation hypothesis. The results indicate that the type of stimulation influences not only when a response is initiated but also how the response is executed. This finding challenges the view, commonly held in mental chronometry, that late motoric processes remain untouched by experimental manipulations. A detailed analysis of the relationship between RT and RF revealed that these variables are not inherently redundant measures, and therefore, RF recording may supplement the traditional RT measurement in mental chronometry. (PsycINFO Database Record (c) 2010 APA, all rights reserved)