Independence of lexical context and phonological information in speech perception.

M. A. Pitt (1995a) studied the joint influence of phonological information and lexical context in W. F. Ganong's (1980) task. Pitt improved on earlier studies by collecting enough observations to make possible the quantitative analyses of an individual's data. The present article shows that the results of such analyses demonstrate that the integration of phonological information and lexical context is very well accounted for by the fuzzy logical model of perception (FLMP). Although Pitt concluded that the results of his research argued against the FLMP in favor of an interactive feedback system, his conclusion was based on an analysis of transformed results. It is argued that this use of a response transformation led to incorrect conclusions and that ultimately, models must be tested directly against observed behavior.

Perceptual adjustments on representations of familiar patterns: change over time and relational features.

Subjects classified individual stimuli as exact copies or as distortions of previously viewed prototype letters. Perceptual adjustments were induced by the presence of difficult (subtle) distortions within the stimulus set. In Experiment 1, subjects initially made feature-based adjustments, and, with experience, adjustments became identity-based. Decisional adjustments also occurred. A similar change over time was obtained in Experiment 2; in addition, the feature-based adjustments could not be explained by overall similarity between letters. Experiment 3 indicated that feature-based adjustments can be long lasting under appropriate circumstances. Experiment 4 indicated that the relevant features are not functionally independent parts of letters, but rather relations between neighboring parts. The results are consistent with the idea that adjustments can change between levels over time, and that the adjusted features are relational in nature.

Dependence, independence, and emergence of word features.

The degree to which a letter is perceived to be an e rather than a c is a function of the central, horizontal bar, which can be made to be more or less present in any given stimulus. By this means, word-form stimuli were produced through the independent, continuous manipulation of e versus c and of r versus h in two word frames (wat-- and --ase) yielding stimuli that ranged between water and watch in the former instance and between erase and chase in the latter. The identification probabilities for these stimuli were well accounted for in each case by a version of a fuzzy propositional model that is based on the assumption of independent features, indicating that the manipulated features within each word frame were not perceptually interdependent. However, the probabilities differed systematically between the two stimulus matrices; this means that there must be some other kind of higher order effect involved in identification. The hypothesis that the interaction was due to an emergent word envelope feature was rejected on the basis of the model analysis.

Evaluation and integration of acoustic features in speech perception.

Identification of synthetic stop consonants as either /bae/, /pae/, /dae/, or /tae/ was examined in two experiments in which the stimuli varied independently on voice onset time (VOT), the consonantal second and third formant (F2-F3) transitions and, in experiment 2, the intensity of the aspiration noise during the VOT period. In both experiments, the patterns of the resulting identification probabilities were complex, but systematic, functions of each of the independent variables. Of most interest was the fact that the likelihood of identifying a stimulus to be /bae/ or /pae/, rather than /dae/ or /tae/, was strongly influenced by the VOT as well as by the F2-F3 transitions. Analogously, the likelihood of identifying a stimulus to be /bae/ or /dae/, rather than /pae/ or /tae/, depended on the F2-F3 transitions as well as on VOT. Three explanations of these results were considered within a fuzzy logical model of speech perception: (1) that there is interaction in the evaluation of acoustic features, (2) that the listener requires more extreme values of acoustic features for some speech sounds than for that of other speech sounds, and (3) that the aspiration noise during the VOT period serves as an independent acoustic feature to distinguish /pae/ and /bae/ from /tae/ and /dae/.

A fuzzy logical model of letter identification.

Stimuli were generated by factorially varying two sets of features that distinguish between two letter patterns. Subjects rated the degree to which each stimulus was an instance of one letter rather than the alternative. The obtained ratings were relatively continuous and systematic functions of the feature manipulations. The results were well accounted for by a model in which (a) each feature has an associated fuzzy predicate that is used to independently evaluate the degree to which it is true that the feature is present in the stimulus; (b) the featural truth values are integrated according to fuzzy logical expressions that correspond directly to propositional descriptions of each letter pattern; and (c) the resulting goodness of match to the stimulus for each letter is compared to that of the alternatives to determine the final identification.

Fuzziness in semantic memory: Choosing exemplars of subjective categories.

Class membership is a fundamental relationship between concepts in semantic memory. Recent research indicates that, class membership may subjectively be a continuous type of relationship. The processing of information about the degree to which items belong to a particular class was investigated in an experiment in which subjects compared two statements describing class membership relationships. The results strongly supported a simple model which describes the judgment process as directly involving subjective degree-of-truthfulness values. The success of the model indicates that the subjects were able to process this kind of fuzzy information in a consistent and systematic manner. Some of the implications of the human competancy for processing fuzzy information are discussed.