An extension of the exemplar-based random-walk model to separable-dimension stimuli

An extension of Nosofsky and Palmeri's (Psychol. Rev. 104 (1997a) 266) exemplar-based random-walk (EBRW) model of categorization is presented as a model of the time course of categorization of separable-dimension stimuli. Nosofsky and Palmeri (1997a) assumed that the perceptual encoding of all stimuli was identical. However, in the current model, we assume as in Lamberts (J. Exp. Psychol.: General 124 (1995) 161) that the inclusion of individual stimulus dimensions into the similarity calculations is a stochastic process with the probability of inclusion based on the perceptual salience of the dimensions. Thus, the exemplars that enter into the random-walk change dynamically during the time course of processing. This model is implemented as a Markov chain. Its predictions are compared with alternative models in a speeded categorization experiment with separable-dimension stimuli.     

Comparing exemplar-retrieval and decision-bound models of speeded perceptual classification

The authors compared the exemplar-based random-walk (EBRW) model of Nosofsky and Palmeri (1997) and the decision-bound model (DBM) of Ashby and Maddox (1994; Maddox & Ashby, 1996) on their ability to predict performance in Garner’s (1974) speeded classification tasks. A key question was the extent to which the models could predict facilitation in the correlated task and interference in the filtering task, in situations involving integral-dimension stimuli. To obtain rigorous constraints for model evaluation, the goal was to fit the detailed structure of the response time (RT) distribution data associated with each individual stimulus in each task. Both models yielded reasonably good global quantitative fits to the RT distribution and accuracy data. However, the DBM failed to properly characterize the interference effects in the filtering task. Apparently, a fundamental limitation of the DBM is that it predicts that the fastest RTs in the filtering task should be faster than the fastest RTs in the control task, whereas the opposite pattern was observed in our data.     

Hierarchical coding in the perception and memory of spatial layouts

Two experiments were performed to investigate the organization of spatial information in perception and memory. Participants were confronted with map-like configurations of objects which were grouped by color (Experiment 1) or shape (Experiment 2) so as to induce cognitive clustering. Two tasks were administered: speeded verification of spatial relations between objects and unspeeded estimation of the Euclidean distance between object pairs. In both experiments, verification times, but not distance estimations, were affected by group membership. Spatial relations of objects belonging to the same color or shape group were verified faster than those of objects from different groups, even if the spatial distance was identical. These results did not depend on whether judgments were based on perceptually available or memorized information, suggesting that perceptual, not memory processes were responsible for the formation of cognitive clusters. Received: 7 October 1999 / Accepted: 17 February 2000     

Effects of similarity and practice on speeded classification response times and accuracies: Further tests of an exemplar-retrieval model

Observers were tested in a perceptual category-learning experiment in which they were instructed to make classification decisions as rapidly as possible without making errors. Nosofsky and Palmeri's (1997b) exemplar-based random walk (EBRW) model of speeded classification was tested for its ability to fit the classification response times and accuracies. The authors demonstrated that the EBRW model provided good quantitative fits to the mean response times and accuracies associated with individual objects as a function of their locations in a multidimensional similarity space and as a function of practice in the task. Preliminary evidence was also obtained that stimulus-specific adjustments in the random walk response criteria may have occurred during the course of learning.     

A model of unidimensional perceptual matching

Faster same than different judgments typically are obtained when two letters are compared. When two tones that might differ only on frequency are compared, however, same judgments typically are slower than different judgments. A uniprocessor, unidimensional model, based on Krueger's noisy-operator theory, was fitted satisfactorily to data from four published studies of tone comparison. The model predicts faster response time on different judgments because of heterogeneity of difference. Because the second tone in a pair typically may be either higher or lower in frequency than the first, there will be a greater variety of perceived difference counts on different pairs than on same pairs. As a result, a large difference count will be decisive and will lead to an immediate "different" response, because it can be produced only by a different pair, whereas a small difference count will not be so decisive because it can be produced by either a same or a different pair. Consequently, there generally will be more rechecking on same than different pairs, and thus longer RT on same pairs.     

Similarity, global matching, and judgments of frequency

In the test-pair similarity effect, forced-choice recognition is more accurate for similar test pairs, such as leopard-cheetah, than it is for unrelated test pairs, such as leopard-turnip. According to global matching models, this occurs because the retrieved familiarities of similar items are correlated. In the Minerva 2 model, global matching underlies frequency judgments as well as recognition memory. One implication of this model is that judged frequencies of similar items should be correlated. Another implication is that judgments of summed frequency for pairs of words (how many presentations were there of word1 and word2 combined?) should have higher variance when word1 and word2 are similar than when they are unrelated. These predictions were tested and confirmed in two experiments. A review of these and other results suggests that theories of recognition memory should also be applicable to frequency-judgment tasks.     

Familiarity and retrieval processes in delayed judgments of learning

Two processes are postulated to underlie delayed judgments of learning (JOLs)--cue familiarity and target retrievability. The two processes are distinguishable because the familiarity-based judgments are thought to be faster than the retrieval-based processes, because only retrieval-based JOLs should enhance the relative accuracy of the correlations between the JOLs and criterion test performance, and because only retrieval-based judgments should enhance memory. To test these predictions, in three experiments, the authors either speeded people's JOLs or allowed them to be unspeeded. The relative accuracy of the JOLs in predicting performance on the criterion test was higher for the unspeeded JOLs than for the speeded JOLs, as predicted. The unspeeded JOL conditions showed enhanced memory as compared with the speeded JOL conditions, as predicted. Finally, the unspeeded JOLs were sensitive to manipulations that modified recallability of the target, whereas the speeded JOLs were selectively sensitive to experimental variations in the familiarity of the cues. Thus, all three of the predictions about the consequences of the two processes potentially underlying delayed JOLs were borne out. A model of the processes underlying delayed JOLs based on these and earlier results is presented.     

Negative priming from masked words: retrospective prime clarification of center-surround inhibition?

Masked repetition and semantic priming effects were examined in 2 experiments. In Experiment 1, a masked-prime lexical decision task followed a phase of detection, semantic, or repetition judgments about masked words. In Experiment 2 participants made speeded pronunciations to target words after they tried to identify masked primes, and the proportion of semantically and identically related prime-target pairs was varied. Center-surround theory CT. H. Carr & D. Dagenbach, 1990; D. Dagenbach, T. H. Carr, & A. Wilhelmsen, 1989) predicts positive repetition priming but negative semantic priming when people attempt, but fail, to extract the meanings of masked words. A retrospective prime-clarification account, in contrast, predicts that semantic and repetition priming effects will vary (being positive or negative) as a function of expectations about the prime-target relation. The data support a retrospective prime-clarification account, which, unlike center-surround theory, correctly predicted negative repetition priming effects.     

Picture-word differences in decision latency: a test of common-coding assumptions

Three experiments examined the processing of pictures and words in two tasks of semantic decision--judgments of conceptual size and judgments of associative relatedness--in order to test the prediction from single-coding models of memory that different semantic decisions produce comparable picture-word latency differences. In Experiment 1 an interaction in decision latency was found such that picture-picture (P-P) pairs were significantly faster than word-word (W-W) pairs in decisions of size but not in decisions of associative relatedness. In Experiment 2 no latency differences were found in decisions of association for pairs presented in P-P, W-W, or mixed (P-W or W-P) forms. Decisions of size, however, were fastest for P-P pairs, intermediate for mixed pairs, and slowest for W-W pairs. In a third experiment, using a speeded inference task, the interaction obtained in the first two experiments was reproduced. In light of these results possible revisions to common-coding assumptions about the processing of pictures and words in semantic decisions are discussed.     

The time course of perception and retrieval in matching and recognition

A four-part experiment was carried out to study the relationship between the time course of object-feature perception and the time course of retrieval of object information from memory. The experiment consisted of 2 perceptual matching tasks, and 2 perceptual recognition tasks. In all 4 tasks, participants provided speeded judgments of the identity of 2 objects. A stochastic feature-sampling model was used to estimate the time needed for feature perception and the time needed for retrieval of feature information. No evidence was found for a systematic relationship between perception times and retrieval times for individual features. Indeed, the model applications indicated that retrieval times were constant for different features, whereas perception rates varied across the features.     

Probing Proctor's priming principle: the effect of simultaneous and sequential presentation on same-different judgments

Three explanations (internal noise, priming, relative frequency) of the fast-same effect were examined. The internal-noise principle, which predicts more errors as well as faster correct judgments on same pairs, was consistently confirmed even with sequential presentation. More elusive was priming, that is, the facilitation of encoding from letter repetition with sequential presentation. Priming was inhibited by the presence of intertrial letter repetition. The error data indicated that priming involves an increased efficiency in encoding (d'), as Proctor claimed, rather than a criterion shift (beta), as Krueger and Shapiro claimed. An alternative to the priming explanation, based on the greater susceptibility of simultaneous presentation to analytical processing, was tested and disconfirmed. Stimulus-set size did not affect the speed advantage for same pairs, thus disconfirming the relative-frequency explanation, according to which same judgments are faster because typically there are fewer unique same than different pairs.     

Item frequency in probe-recognition memory search: Converging evidence for a role of item-response learning

In short-term probe-recognition tasks, observers make speeded old–new recognition judgments for items that are members of short lists. However, long-term memory (LTM) for items from previous lists influences current-list performance. The current experiment pursued the nature of these long-term influences—in particular, whether they emerged from item-familiarity or item-response-learning mechanisms. Subjects engaged in varied-mapping (VM) and consistent-mapping (CM) short-term probe-recognition tasks (e.g., Schneider & Shiffrin, Psychological Review, 84, 1–66, 1977). The key manipulation was to vary the frequency with which individual items were presented across trials. We observed a striking dissociation: Whereas increased presentation frequency led to benefits in performance for both old and new test probes in CM search, it resulted in interference effects for both old and new test probes in VM search. Formal modeling suggested that a form of item-response learning took place in both conditions: Each presentation of a test probe led to the storage of that test probe—along with its associated “old” or “new” response—as an exemplar in LTM. These item-response pairs were retrieved along with current-list items in driving observers’ old-– recognition judgments. We conclude that item-response learning is a core component of the LTM mechanisms that influence CM and VM memory search.     

Perceptual processes in matching and recognition of complex pictures

The role of perceptual feature sampling in speeded matching and recognition was explored in 4 experiments. Experiments 1-3 involved a perceptual matching task with pictures of various objects and scenes. In Experiments 2 and 3, same-different judgments were given under time pressure. The main objective of the matching task was to obtain measures of the perceptual processing rates of different object features. Experiment 4 was an old-new recognition experiment, in which the same stimuli as those in the matching task were used. Response signals were used to limit processing time in the recognition task. The results demonstrated that it is possible to predict speeded recognition performance from performance in perceptual matching. A simple stochastic feature-sampling model provides a unified account of the data from the 4 experiments.     

Object-based selection within and beyond the focus of spatial attention

In a series of experiments, we examined the effect of perceptual objects on visual attentional processing in the presence of spatially cued attentional selection. Subjects made speeded judgments about two visual elements that were either both on the same object or on two different objects. Judgments were faster when the elements were on the same object than when they were on different objects, revealing an object advantage. Importantly, the object advantage remained even when either exogenous or endogenous spatial cues were used to direct the subjects' attention to a part of the display, contrary to earlier findings of other researchers. The object advantage, however, did disappear when the stimulus duration was shortened substantially. The results show that object-based selection is pervasive and is not diminished by the act of selective attention. The results are discussed in terms of their implications for the mechanisms that underlie attentional selection.     

Recognition memory ROCs for item and associative information: The contribution of recollection and familiarity

Receiver-operating characteristics (ROCs) were examined in three recognition memory experiments. ROCs for item information (i.e., was this word presented?) were found to be curvilinear. However, ROCs for associative information (i.e., were these two words presented together?) were found to be linear. The results are in agreement with the predictions of a dual-process model that assumes that recognition judgments are -based on familiarity and recollection. Familiarity reflects the assessment of a continuous strength dimension and is well described as a signal detection process, whereas recollection reflects the retrieval of qualitative information about the study episode and behaves like a discrete threshold process. The results showed that memory judgments about items relied on a combination of recollection and familiarity, but that judgments about associations relied primarily on recollection. Further examination of the associative ROCs suggested that subjects were able to recollect that old pairs of items were in the study list, and, under some conditions, that new pairs were not in the study list.     

Large,colorful, or noisy? Attribute- and modality-specific activations during retrieval of perceptual attribute knowledge

Position emission tomography was used to investigate whether retrieval of perceptual knowledge from long-term memory activates unique cortical regions associated with the modality and/or attribute type retrieved. Knowledge about the typical color, size, and sound of common objects and animals was probed, in response to written words naming the objects. Relative to a nonsemantic control task, all the attribute judgments activated similar left temporal and frontal regions. Visual (color, size) knowledge selectively activated the right posterior inferior temporal (PIT) cortex, whereas sound judgments elicited selective activation in the left posterior superior temporal gyrus and the adjacent parietal cortex. All of the attribute judgments activated a left PIT region, but color retrieval generated more activation in this area. Size judgments activated the right medial parietal cortex. These results indicate that the retrieval of perceptual semantic information activates not only a general semantic network, but also cortical areas specialized for the modality and attribute type of the knowledge retrieved.     

Fluent, fast, and frugal? A formal model evaluation of the interplay between memory, fluency, and comparative judgments

A new process model of the interplay between memory and judgment processes was recently suggested, assuming that retrieval fluency-that is, the speed with which objects are recognized-will determine inferences concerning such objects in a single-cue fashion. This aspect of the fluency heuristic, an extension of the recognition heuristic, has remained largely untested due to methodological difficulties. To overcome the latter, we propose a measurement model from the class of multinomial processing tree models that can estimate true single-cue reliance on recognition and retrieval fluency. We applied this model to aggregate and individual data from a probabilistic inference experiment and considered both goodness of fit and model complexity to evaluate different hypotheses. The results were relatively clear-cut, revealing that the fluency heuristic is an unlikely candidate for describing comparative judgments concerning recognized objects. These findings are discussed in light of a broader theoretical view on the interplay of memory and judgment processes.     

Response reversals in recognition memory

Using a dynamic sequential sampling model and a recently proposed model for confidence judgments in recognition memory (T. Van Zandt, 2000b), the authors examine the tendency for rememberers to reverse their responses after a primary decision. In 4 experiments, speeded "old"-"new" decisions were made under bias followed by a 2nd response', either a confidence judgment or another simple choice. The data from these experiments showed that participants know when they have made a mistake and that they respond to this knowledge by reversing their responses. Response reversals are thus shown to be important for constructing models of the response-selection process in recognition memory.     

Units of phonological recoding of word-like stimuli used by children and adults

Third-grade, sixth-grade, and coUege-age subjects performed a “same”-“different” task, using a phonological identity criterion for visually presented pseudowords. Consistent with Krueger’s (1978) model of single-glance “same”-“different” judgments, judgments of phonologically matching stimuli were made more quickly and less accurately than were judgments of phonologically nonmatching stimuli, and error rates and RTs were longer for phonologically similar nonmatching pairs than for phonologically dissimilar nonmatching pairs. It was concluded that subjects of all ages tested could process phonologically recoded information in a holistic fashion, and the implications of these conclusions with respect to reading processes are discussed.