The free classification of analyzable and unanalyzable stimuli

The free classification of two-dimensional analyzable and unanalyzable stimuli was investigated. Analyzable stimuli consist of dimensions which are distinct and phenomenally separable (e.g., colored geometric forms); unanalyzable stimuli consist of two dimensions which are not distinct, not phenomenally separable, and which are probably perceived as a unitary dimension (e.g., Munsell colors). In the first experiment, Ss judged the similarity between each stimulus pair for both types of stimuli. The results replicated previous work in showing that the city-block metric was appropriate for the analyzable stimuli and that the euclidean metric was appropriate for unanalyzable stimuli. In the second experiment, Ss classified sets of analyzable and unanalyzable stimuli into two or three groups in any way they wished. For analyzable stimuli, classification was based on the dimensional structure-stimuli which alter the dimensional structure by defining another dimension change classification. For unanalyzable stimuli, classification was based on the similarity structure-stimuli which alter the similarity structure change classification.     

Classification of sets of stimuli with different stimulus characteristics and numerical properties

The purpose of this experiment was to determine the effects of stimulus characteristics and numerical properties of sets of stimuli on classification. Sets contained12 stimuli which were all identical, had different categories defined by color, or had different categories defined by attributes of color and size. Number of categories and numerical distribution of stimuli in categories were varied. For each set S made a free classification and several restricted classifications in which the number of classes was specified. The results show: Sets of identical stimuli are classified into equal sized groups. Categorically defined stimuli are classified by category insofar as possible, but the tendency to numerical balance affects classificlltions with unbalanced numerical distributions or when the task restriction is incompatible with category classification. Stimuli defined by attributes are classified so as to maintain the attribute structure, although both category classification and numerical balance tendencies are evident with unbalanced numerical distributions and incompatible classification restrictions.     

Effects of focusing strategy on speeded classification with grouping,filtering, and condensation tasks

Speeded classification was studied with three tasks varying in the way in which extra stimuli are provided for a single class:grouping, with additional levels on a single relevant dimension;filtering, with additional levels on an irrelevant dimension; andcondensation, with additional levels on a second relevant dimension. (Both relevant dimensions must be processed for correct classification.) For the dimensions used (color and form), filtering was easiest, followed by grouping and condensation. In the latter two cases, asymmetric classifications, in which one class had a single member, eliminated the difficulty of classification. The presumed mechanism is focusing, in which the single stimulus is seen as a positive set and all other stimuli as negative.     

Right or wrong, familiar or novel in pictorial list discrimination learning

The interaction between nonassociative learning (presentation frequencies) and associative learning (reinforcement rates) in stimulus discrimination performance was investigated. Subjects were taught to discriminate lists of visual pattern pairs. When they chose the stimulus designated as right they were symbolically rewarded and when they chose the stimulus designated as wrong they were symbolically penalised. Subjects first learned one list and then another list. For a "right" group the pairs of the second list consisted of right stimuli from the first list and of novel wrong stimuli. For a "wrong" group it was the other way round. The right group transferred some discriminatory performance from the first to the second list while the control and wrong groups initially only performed near chance with the second list. When the first list involved wrong stimuli presented twice as frequently as right stimuli, the wrong group exhibited a better transfer than the right group. In a final experiment subjects learned lists which consisted of frequent right stimuli paired with scarce wrong stimuli and frequent wrong stimuli paired with scarce right stimuli. In later test trials these stimuli were shown in new combinations and additionally combined with novel stimuli. Subjects preferred to choose the most rewarded stimuli and to avoid the most penalised stimuli when the test pairs included at least one frequent stimulus. With scarce/scarce or scarce/novel stimulus combinations they performed less well or even chose randomly. A simple mathematical model that ascribes stimulus choices to a Cartesian combination of stimulus frequency and stimulus value succeeds in matching all these results with satisfactory precision.     

The effects of sequential presentation and spatial arrangements on the free classification of multidimensional stimuli

Subjects classified sets of eight stimuli, constructed from three binary dimensions, into discrete groups in any way they wished. The stimuli were presented either simultaneously (all atonce) or sequentially (one at a time). When stimuli were presented simultaneously, different spatial arrangements did not produce different classifications. When stimuli were presented sequentially, in some sequential orders the level of each dimension varied at a different position in the sequence. For these orders, Ss tended to use the two levels of the first dimension that varied to classify the stimuli into two groups. But, other orders in which the levels of all dimensions varied on the second stimulus did not influence Ss’ classification. A comparison of sequential and simultaneous presentation showed for sequential presentation: (a) a smaller number of classifications was made using the dimensional structure to classify the stimuli, and (b)of those classifications that were dimensional, fewer dimensions were used to classify the stimuli into groups.     

Holistic vs. attribute repetition effects in classifying stimuli

The effect of the just previous stimulus on the current response was determined in three speeded classification experiments. When the stimuli were perceptual patterns, and when they were words, there was marked facilitation if the previous stimulus was identical to the current stimulus. When successive perceptual stimuli were composed of identical elements, but in a changed configuration, there was no measureable sequential effect on “same” response times. These results are for integral stimuli. When stimuli are not integral, as with some studies in the literature, it is suggested that each two-dimensional nonintegral stimulus is treated by the observer as two objects. In those cases, responses can be facilitated by repetition of that object on which responses were based on the previous trial, and this can occur when a value of the other dimensions (other objects) has not repeated. Accordingly, the processing of integral and nonintegral stimuli must be considered separately when attempting to evaluate process models. Further, facilitation due to stimulus repetitions does not account for all of the differences in response times between various classification tasks. These additional differences may be attributed to a multidimensional range effect analogous to the range effects found in psychophysical tasks.     

Free classification: Element-level and subgroup-level similarity

Subjects classified sets of multidimensional stimuli into two groups in any way they wished. The sets were composed of 6 or 12 stimuli: 2 or 4 instances of 3 different stimuli (e.g., 2 blue circles, 2 green circles, 2 red circles). There were striking individual differences in the preferred classification. Some subjects maximized the similarity between subgroups by matching the composition of the subgroups--one instance of each stimulus was placed in each group. The other subjects maximized the similarity among stimuli within each subgroup by placing similar stimuli in each group (the blues and greens in one group, the reds in the other). The nature of the stimuli as well as the relationships among the three stimuli had little effect on classification. In this case, cognitive styles specific to individuals but general across diverse dimensions and stimulus sets determined classification.     

Clustering, seriation, and subset extraction of confusion data

The study of confusion data is a well established practice in psychology. Although many types of analytical approaches for confusion data are available, among the most common methods are the extraction of 1 or more subsets of stimuli, the partitioning of the complete stimulus set into distinct groups, and the ordering of the stimulus set. Although standard commercial software packages can sometimes facilitate these types of analyses, they are not guaranteed to produce optimal solutions. The authors present a MATLAB *.m file for preprocessing confusion matrices, which includes fitting of the similarity-choice model. Two additional MATLAB programs are available for optimally clustering stimuli on the basis of confusion data. The authors also developed programs for optimally ordering stimuli and extracting subsets of stimuli using information from confusion matrices. Together, these programs provide several pragmatic alternatives for the applied researcher when analyzing confusion data. Although the programs are described within the context of confusion data, they are also amenable to other types of proximity data.     

Monkeys (Macaca mulatta and Cebus apella) track, enumerate, and compare multiple sets of moving items

Despite many demonstrations of numerical competence in nonhuman animals, little is known about how well animals enumerate moving stimuli. In this series of experiments, rhesus monkeys (Macaca mulatta) and capuchin monkeys (Cebus apella) performed computerized tasks in which they had to enumerate sets of stimuli. In Experiment 1, rhesus monkeys compared two sets of moving stimuli. Experiment 2 required comparisons of a moving set and a static set. Experiment 3 included human participants and capuchin monkeys to assess all 3 species' performance and to determine whether responding was to the numerical properties of the stimulus sets rather than to some other stimulus property such as cumulative area. Experiment 4 required both monkey species to enumerate subsets of each moving array. In all experiments, monkeys performed above chance levels, and their responses were controlled by the number of items in the arrays as opposed to nonnumerical stimulus dimensions. Rhesus monkeys performed comparably to adult humans when directly compared although capuchin performance was lower.     

The influence of stimulus uncertainty and experimental instructions on visual selection

The looking behavior of adults and children was recorded while they viewed pairs of stimuli differing in stimulus uncertainty. Ss in one experimental group were encouraged to identify the stimuli and indicate whether they had been seen in a previous phase of the experiment. For the remaining Ss, instructions minimized the importance of the stimuli to the experiment. Results indicate that, when stimulus uncertainty was influential, the relationship between stimulus uncertainty and looking time was monotonically increasing. However, stimulus uncertainty was an effective determinant of looking behavior only when Ss were motivated to identify the stimuli. The behavior of adults and children did not differ.     

两种学习模式下类别学习的结果：原型和样例

利用“学习－迁移”的任务范式和单一特征类别判断技术,探讨了分类和推理两种类别学习模式的结果,比较了两种学习模式的效果和策略。研究表明：两种学习模式产生了不同的结果,分类学习的结果是样例,推理学习的结果是原型;在学习效果方面,分类学习比推理学习在达标比例上更高,但在进度上差异不显著;在策略运用方面,分类学习比推理学习更快地使用单维度策略,而在高水平策略的运用上,两者差异不显著     

The effect of correlated linguistic dimensions on speeded classification of visually presented trigrams

The influence of two types of linguistic dimensions, word-nonword and consonant pronunciation, on classification speed of trigrams in card-sorting tasks of two levels of complexity was examined. In complex grouping tasks, which required the evaluation of more than one letter to classify each stimulus, sorting times were faster when the linguistic dimension was correlated with, rather than orthogonal to, the response categories. For tasks in which each stimulus could be classified on the basis of a single letter, no effect of the correlated vs orthogonal linguistic dimension was observed, even when performance was degraded by visual noise. These results provide further evidence that, while linguistic properties of visual stimuli may influence classification time in complex tasks, they are of little importance in the performance of tasks only requiring the discriminalion of a single visual feature.     

Reinforcer frequency and restricted stimulus control.

Stimulus control was evaluated in 3 individuals with moderate to severe mental retardation by delayed identity matching-to-sample procedures that presented either one or two discrete forms as sample stimuli on each trial. On pretests, accuracy scores on one-sample trials were uniformly high. On two-sample trials, the correct stimulus (i.e., the one that subsequently appeared in the comparison array) varied unpredictably, and accuracy scores were substantially lower, suggesting that both sample stimuli did not exert stimulus control on every trial. Subjects were then given training sessions with the one-sample task and with a new set of four stimuli. For two of the stimuli, correct matching responses were followed by reinforcers on a variable-ratio schedule that led to a high reinforcer rate. For the other two stimuli, correct responses were followed by reinforcers on a variable-ratio schedule that led to a substantially lower reinforcer rate. Results on two-sample tests that followed showed that (a) on trials in which comparison arrays consisted of one high reinforcer-rate and one low reinforcer-rate stimulus, subjects most often selected the high-rate stimulus; and (b) on trials in which the comparison arrays were either two high reinforcer-rate stimuli or two low reinforcer-rate stimuli and the samples were one high reinforcer- and one low reinforcer-rate stimulus, accuracy was higher on trials with the high-rate comparisons. These results indicate that the frequency of stimulus control by high reinforcer-rate samples was greater than that by low reinforcer-rate samples. Following more training with the one-sample task and reversed reinforcement schedules for all stimuli, the differences in stimulus control frequencies on two-sample tests also reversed. These results demonstrate experimental control by reinforcement contingencies of which of two sample stimuli controlled selections in the two-sample task. The procedures and results may prove to be relevant for understanding restricted stimulus control and stimulus overselectivity.     

The impact of category structure and training methodology on learning and generalizing within-category representations

When interacting with categories, representations focused on within-category relationships are often learned, but the conditions promoting within-category representations and their generalizability are unclear. We report the results of three experiments investigating the impact of category structure and training methodology on the learning and generalization of within-category representations (i.e., correlational structure). Participants were trained on either rule-based or information-integration structures using classification (Is the stimulus a member of Category A or Category B?), concept (e.g., Is the stimulus a member of Category A, Yes or No?), or inference (infer the missing component of the stimulus from a given category) and then tested on either an inference task (Experiments 1 and 2) or a classification task (Experiment 3). For the information-integration structure, within-category representations were consistently learned, could be generalized to novel stimuli, and could be generalized to support inference at test. For the rule-based structure, extended inference training resulted in generalization to novel stimuli (Experiment 2) and inference training resulted in generalization to classification (Experiment 3). These data help to clarify the conditions under which within-category representations can be learned. Moreover, these results make an important contribution in highlighting the impact of category structure and training methodology on the generalization of categorical knowledge.     

Salience of stimulus and response features in choice-reaction tasks.

A pattern of differential reaction time (RT) benefits obtained in spatial-precuing tasks has been attributed to translation processes that operate on mental codes formed to represent the stimulus and response sets. According to the salient-features coding principle, the codes are based on the salient stimulus and response features, with RTs being fastest when the two sets of features correspond. Three experiments are reported in which the stimulus and response sets were manipulated using Gestalt grouping principles. In the first two experiments, stimuli and responses were grouped according to spatial proximity, whereas in the last experiment, they were grouped according to similarity. With both types of manipulations, the grouping of the stimulus set systematically affected the pattern of precuing benefits. Thus, in these experiments, the organization of the stimulus set was the primary determinant of the features selected for coding the stimulus and response sets in the translation process.     

The effects of stimulus type,training, and chronological age on children's identification and recoding of multidimensional stimuli

Kindergarten and second-grade children (75 and 99 months of age, respectively) were first taught that the two stimuli within each of four pairs of multidimentional stimuli differed with respect to their values on every one of three bivalued dimensions: color, size, and form. Each of the eight stimuli was then presented twice, one at a time, and the child was asked either to find its duplicate (eight encoding trials) or to find its complementary mate (eight recoding trials) among the complete set of eight stimuli. Next, each of the eight stimulus compounds was presented twice as a display stimulus for 5 sec and, after a delay of 10 to 15 sec, the child was asked to find the display stimulus (eight trials of encoding plus memory) or its complement (eight trials of recoding plus memory) among the complete set. The stimuli for half the children in each age group were standard unitary compounds (e.g., a large red circle, a small blue square, etc.) and for the other half they were partitioned stimuli with their dimensional values spatially separated (e.g., large arrow, circle outline, and patch of color). Half of the children in each of these subgroups were given a basic pretraining, and the other half received extended pretraining, in recoding the stimulus attributes. The results indicated that unitary stimuli were easier to encode but the partitioned stimuli were easier to recode, that recoding was much more difficult than encoding, that extended training improved recoding performance, and that second graders were slightly better at encoding and much better at recoding than the kindergarten children. The patterns of performance on the tasks involving memory were similar to those just described. The results were discussed in terms of children's abilities to analyze multidimensional stimuli into their dimensional components.     

Space, object, and task selection

Within the field of selective attention, two separate literatures have developed, one examining the effect of selection of objects and another examining the effect of selection of features. The present study bridged these two traditions by examining the compatibility effects generated by two features of attended and unattended nontarget (foil) stimuli. On each trial, participants determined either the identity or the orientation of a visual stimulus. Spatial attention was controlled using cues (presented prior to the target frame) designed to involuntarily capture attention. We independently manipulated the stimulus dimension the participants prepared for and the stimulus dimension on which they actually executed the task. Preparation had little influence on the magnitude of compatibility effects from foil stimuli. For attended stimuli, the stimulus dimension used in executing the task produced large compatibility effects, regardless of whether that dimension was prepared. These and other compatibility effects (e.g., Stroop effects) are discussed in relation to an integrative model of attentional selection. The key assumptions are that (1) selection occurs at three distinct levels (space, object, and task), (2) spatial attention leads to semantic processing of all dimensions, and (3) features do not automatically activate responses unless that object is selected for action.     

Naming and categorization in young children: III. Vocal tact training and transfer of function

Following pretraining with everyday objects, 10 children aged from 1 to 4 years were given common vocal tact training with a set of three pairs of arbitrary stimuli of differing shapes; Set 1. Nine children learned to tact one stimulus as "zog" and the other as "vek" in each pair, and all passed subsequent pairwise tests for the corresponding listener behavior to each listener stimulus (i.e., /zog/ and /vek/, respectively). The children were next trained to clap to one stimulus of Pair 1 and wave to the other, and all then showed name-consistent transfer of these behaviors to the stimuli of Pair 2 and Pair 3. Seven children also were given a test of listener responding to experimenter-modeled clap and wave gestures, respectively, which they all passed. Four of the children next participated in a category match-to-sample test for the Set 1 stimuli; all 4 passed. For each pair of two additional six-stimuli sets, Set 2 and Set 3, 3 children were trained to wave to one stimulus and to clap to the other. For each set, all 3 children showed perfect transfer of the vocal tacts trained to Set 1, and of listener behavior both to the auditory stimuli /zog/ and /vek/ and to experimenter-modeled clap and wave gestures. They also sorted the stimuli perfectly in category match-to-sample tests for Set 2, Sets 1 and 2 combined, Set 3, and Sets 1, 2, and 3 combined. The results show that even in very young children, naming is a powerful means of generating new category relations among as many as 18 arbitrary stimuli.