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.     

A diffusion model analysis of the effects of aging on letter discrimination

The effects of aging on accuracy and response time were examined in a letter discrimination experiment with young and older subjects. Results showed that older subjects (ages 60-75) were generally slower and less accurate than young subjects. R. Ratcliff's (1978) diffusion model was fit to the data, and it provided a good account of response times, their distributions, and response accuracy. The results produce similar age effects on the nondecision components of response time (about 50 ms slowing) and the response criteria (more conservative settings) to those from R. Ratcliff, A. Thapar, and G. McKoon (2001), but also show a reduced rate of accumulation of evidence for older subjects. The model-based approach has the advantage of allowing the separation of aging effects on different components of processing.     

The effects of aging on reaction time in a signal detection task

The effects of aging on response time are examined in 2 simple signal detection tasks with young and older subjects (age 60 years and older). Older subjects were generally slower than young subjects, and standard Brinley plot analyses of response times showed typical results: slopes greater than 1 and (mostly) negative intercepts. R. Ratcliff, D. Spieler, and G. McKoon (2000) showed that the slopes of Brinley plots measure the relative standard deviations of the distributions of response times for older versus young subjects. Applying R. Ratcliff's (1978) diffusion model to fit the response times, their distributions, and response accuracy, it was found that the larger spread in older subjects' response times and their slowness relative to young subjects comes from a 50-ms slowing of the nondecision components of response time and more from conservative settings of response criteria.     

Task-invariant aspects of goodness in perceptual representation.

In two experiments, pairs of Garner's classical 5-dot patterns were presented with an interstimulus interval of 500 ms in a same-different task in which a physical sameness criterion was used: Rotated or reflected versions of the same pattern were rated as different. Patterns varied in "goodness" according to Garner's equivalence set size measure. Both first and second pattern goodness affected reaction time and accuracy. This result and fits of models to reaction time data indicate that equivalence set representations are used in the task, as in a related categorical matching task in previous studies. Two effects were observed that contrast with the categorical matching task: One is a conflict between the need to respond different to patterns that are categorically equivalent under the equivalence set representation; the other is that extra time is needed for rechecking of the representation if pattern structures are hard to distinguish. In combination with previous studies, the present results show that even though the processes differ, the same representational mechanism is used across tasks.     

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).     

Feature lists and confusion matrices

This report compares three feature list sets for capital letters, previously proposed by different investigators, on the ability of each to predict empirical confusion matrices. Toward this end, several variants of assumed information processes in recognition were also compared. The best model incorporated: (1) variable feature retrieval probabilities, (2) a goodness-of-match lower threshold below which guessing determines response, and (3) response bias on guessing trials. This model, when combined with one particular proposed feature list set, produced stress values of less than 9% in comparisons to empirical matrices for each of three different Ss. The feature retrieval probability vectors associated with these minimum-stress predictions were highly correlated ( \(\bar r = .83\) ), suggesting considerable generality of process and feature sets between Ss.     

Object identification: The mental representation of physical and conceptual attributes

In two experiments, subjects indicated whether two pictures of familiar objects were equivalent. The picture pairs were identical, showed the same object in various perspectives and states, or showed different objects with varying degrees of conceptual relatedness. In Experiment 1, the equivalence criterion for judging the picture pairs was varied between subjects (identity of pictures; conceptual equivalence of objects at subordinate, basic, or superordinate level). The reaction times of the four subject groups suggest that a pictorial stimulus is not always mentally represented in the same way, and that the instructions given determine which attributes of the stimulus are represented. In Experiment 2, the visual similarity of the picture pairs was varied. The results indicate, at least with a basic-level equivalence instruction, that not only perceptual, but also non-perceptual, functional attributes are represented—namely, those that, according to Rosch et al. (1976), are common to the members of a superordinate category.     

Influence of sensitivity on response bias in taste and audition

A detection theoretic analysis was employed to examine sensitivity and response bias in two modalities. In Experiment 1, 6 tasters made same-different judgments about the concentration of either sucrose or quinine in pairs of tonic water samples. The beverages were colored, but color was not predictive of the concentration of the sweet or bitter ingredient. When same-different ratings were collapsed to approximate the outcome of a categorical decision, tasters with poorer sensitivity appear to have adopted more extreme response criteria than did tasters with greater sensitivity, irrespective of taste quality, color, or whether pairs of solutions comprised the same or different colors. In Experiment 2, 3 individuals discriminated pairs of 1000-Hz sinusoids differing in amplitude. Six amplitude differences were tested. Rating-scale versions of two paradigms: The single-interval yes-no task and the two-interval same-different task were used to measure sensitivity and bias. There was a preponderance of "same" responses in the same-different task. Estimates of bias obtained from collapsed ratings in both tasks were unaffected by sensitivity, but a consideration of the range over which sets of criteria were spread suggested a general tendency toward more conservative response biases as sensitivity declined.     

Word concreteness and encoding effects on context-dependent discrimination

In three experiments, we investigated the effects of word concreteness and encoding instructions on context-dependent discrimination in verbal contexts, using Murnane, Phelps, and Malmberg's (1999) ICE (item, context, ensemble) theory as the framework Word concreteness was manipulated within participants, and encoding was manipulated between participants. It was hypothesized that the magnitude of context-dependent discrimination would be affected by both concreteness and encoding instructions. Imagery instructions resulted in context-dependent discrimination for both concrete and abstract word pairs across all the experiments. Context-dependent discrimination was observed under rote instructions for concrete and abstract words, particularly when the same context word was paired multiple times with the targets. The results indicated that context-dependent discrimination is not dependent solely on the use of interactive imagery instructions or on word concreteness.     

Effects of instructions and drug administration on temporal resolution of paired flashes

Sixteen male alcoholics were shown pairs of light flashes separated by intervals ranging from 0 to 100 msec., and judged whether there were one or two flashes. Two-flash fusion theshold (TFT) was raised by administration of promazine hydrochloride, a tranquilizing drug, and was higher for strict than for lenient instructions. Signal detection analysis showed that the drug reduced sensitivity but did not affect criterion, while instructions altered criterion placement without changing sensitivity.     

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, 1979b), 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.     

Interpreting the parameters of the diffusion model: an empirical validation

The diffusion model (Ratcliff, 1978) allows for the statistical separation of different components of a speeded binary decision process (decision threshold, bias, information uptake, and motor response). These components are represented by different parameters of the model. Two experiments were conducted to test the interpretational validity of the parameters. Using a color discrimination task, we investigated whether experimental manipulations of specific aspects of the decision process had specific effects on the corresponding parameters in a diffusion model data analysis (see Ratcliff, 2002; Ratcliff & Rouder, 1998; Ratcliff, Thapar, & McKoon, 2001, 2003). In support of the model, we found that (1) decision thresholds were higher when we induced accuracy motivation, (2) drift rates (i.e., information uptake) were lower when stimuli were harder to discriminate, (3) the motor components were increased when a more difficult form of response was required, and (4) the process was biased toward rewarded responses.     

Evidence that thesame-different disparity in letter matching is not attributable to response bias

When pairs of letters or letter strings are judged assame ordifferent, correctsame responses are usually faster than correctdifferent responses. Recently, Ratcliff and Hacker (1981, 1982) have argued that thissame-different disparity is likely attributable solely to a bias to respondsame. The present article reports an experiment in which the relative bias to respondsame ordifferent was varied for matches of single-letter pairs. Bias was manipulated by having 80, 60, 40, or 20 pairs in a block of 100 besame, with the remainder beingdifferent. For both sequential and simultaneous presentation of the letters,same reaction times had an overall advantage overdifferent reaction times that could not be attributed to response bias. Moreover, consistent with Proctor’s (1981) facilitation principle, this reaction time disparity was greater with sequential presentation than with simultaneous presentation. The larger reaction time advantage forsame pairs with sequential presentation was obtained without an increase in the relative number of false-same responses, supporting the view that the facilitation is attributable to changes in sensitivity and not to changes in encoding criteria.     

A diffusion model account of response time and accuracy in a brightness discrimination task: fitting real data and failing to fit fake but plausible data

A brightness discrimination experiment was performed to examine how subjects decide whether a patch of pixels is “bright” or “dark,” and stimulus duration, brightness, and speed versus accuracy instructions were manipulated. The diffusion model (Ratcliff, 1978) was fit to the data, and it accounted for all the dependent variables: mean correct and error response times, the shapes of response time distributions for correct and error responses, and accuracy values. Speed-accuracy manipulations affected only boundary separation (response criteria settings) in the model. Drift rate (the rate of accumulation of evidence) in the diffusion model, which represents stimulus quality, increased as a function of stimulus duration and stimulus brightness but asymptoted as stimulus duration increased from 100 to 150 msec. To address the argument that the diffusion model can fit any pattern of data, simulated patterns of plausible data are presented that the model cannot fit.     

Influence of category identity on letter matching: conceptual penetration of visual processing or response competition?

Participants performed same-different matching tasks, with physical-identity instructions, on letter pairs composed from the letters B, b, and p. The letters in a pair were presented simultaneously or sequentially, with the experiments differing in whether (1) the letters could appear in two or four positions, (2) two or five SOAs were used, (3) the font was Arial or one in which the two loops of the letter B were of the same size, and (4) p did or did not occur in same pairs. With sequential presentation, different RTs were longer when the letters had the same name (Bb; within-category pair) than when they did not (Bp; between-category pair), replicating a finding by Lupyan et al. (2010). However, unlike in their study, this category effect was also significant with simultaneous presentation, tending to be nonsignificantly smaller for RTs but larger for accuracy than that obtained with sequential presentation. A similar pattern was observed when we removed a bias to respond different whenever the letter p was detected in the experiments in which p did not appear in same pairs. The presence of a category effect with simultaneous presentation is predicted by a response competition account, but not by Lupyan et al.'s conceptual-penetration-of-visual-processing account.     

Scale convergence as a criterion for rescaling: Information integration with difference,ratio, and averaging tasks

Ss lifted pairs of weights simultaneously, one in each hand, and judged either the difference, ratio, or average heaviness of the two weights. Data for the difference and ratio tasks were in general agreement with subtractive and ratio models, but the averaging data showed discrepancies from the constant-weight averaging model similar to those reported in previous psychophysical research. Rescaling was ruled out for the averaging data, because responses to pairs of equal weight were a linear function of subtractive model scale values derived from the difference task data. Scale values for the ratio and difference task data were related exponentially, as were the responses to the pairs, consistent with Torgerson’s conjecture that Ss do not distinguish “differences” from “ratios.” They appear to use the same composition rule but different output functions, depending on the procedures for responding. The scale convergence criterion can thus prevent inappropriate rescaling when a model fails and can dictate rescaling even when a model fits.     

The effects of divided attention on encoding processes under incidental and intentional learning instructions: Underlying mechanisms?

Divided attention (DA) at encoding has been shown to significantly disrupt later memory for the studied information. However, what type of processing gets disrupted during DA remains unresolved. In this study, we assessed the degree to which strategic effortful processes are affected under DA by comparing the effects of DA at encoding under intentional and pure incidental learning instructions. In three experiments, participants studied list of words or word pairs under either full or divided attention. Results of three experiments, which used different methodologies, converged to show that the effects of DA at encoding reduce memory performance to the same degree under incidental and intentional learning. Secondary task performance indicated that encoding under intentional learning instructions was more effortful than under incidental learning instructions. In addition, the results indicated enhanced attention to the initial appearance of the words under both types of learning instructions. Results are interpreted to imply that other processes, rather than only strategic effortful ones, might be affected by DA at encoding.     

异同比较中的维度转移效应

以有颜色的实心几何图形为刺激材料进行了4个实验,考察异同比较中异反应之间的序列效应,被试为北京农业工程大学本科生77名。实验1a和1b中前后刺激对完全平衡,而实验2a和2b中前后刺激对随机平衡。实验1a,2a和2b发现了维度转移效应,表现为对于异反应后的异反应,前后2次异反应的差异维度一致时的反应快于不一致时的反应。本文以认知神经科学已有的相关证据解释了该效应产生的原因,并指出该效应反映了选择性注意在异反应判断中起重要作用,而且当任务要求注意在刺激维度上的分配不断变化时,注意按照当前刺激的特点做实时的分配     

Estimating parameters of the diffusion model: approaches to dealing with contaminant reaction times and parameter variability

Three methods for fitting the diffusion model (Ratcliff, 1978) to experimental data are examined. Sets of simulated data were generated with known parameter values, and from fits of the model, we found that the maximum likelihood method was better than the chi-square and weighted least squares methods by criteria of bias in the parameters relative to the parameter values used to generate the data and standard deviations in the parameter estimates. The standard deviations in the parameter values can be used as measures of the variability in parameter estimates from fits to experimental data. We introduced contaminant reaction times and variability into the other components of processing besides the decision process and found that the maximum likelihood and chi-square methods failed, sometimes dramatically. But the weighted least squares method was robust to these two factors. We then present results from modifications of the maximum likelihood and chi-square methods, in which these factors are explicitly modeled, and show that the parameter values of the diffusion model are recovered well. We argue that explicit modeling is an important method for addressing contaminants and variability in nondecision processes and that it can be applied in any theoretical approach to modeling reaction time.