Stimulus context and duration discrimination

The ability of human observers to discriminate duration was assessed in two types of tasks: (1) pulse tasks, in which the observer compared the duration of two brief increments in an ongoing sinusoid, and (2) gap tasks, in which the observer compared the duration of two brief interruptions in an ongoing sinusoid. Performance in these tasks was assessed in three different contexts: noise alone, noise plus continuous sinusoids, and noise plus continuous sinusoids chosen to induce a pitch segregation effect. Performance in the pulse task was independent of the changes in context; however, performance in the gap task changed as a function of context condition. There was a large decrement in the observers’ ability to discriminate duration when the stimulus ensemble induced the pitch segregation effect. The results are discussed in terms of the relationship between duration discrimination and stimulus variations which do not carry duration information.     

Stimulus context and infant orientation discrimination

In three experiments, the effect of additional "contextual" elements on the discrimination of the orientation of linear and curvilinear segments was investigated with 4-month-old infants. In Experiment 1, paired visual matrices (one which contained some irregularity in orientation of internal elements, vs one which contained no irregularities) were presented. Infants detected irregular matrices significantly better than chance, but such detection was not aided by contextual elements. Discrimination of orientation in Experiment 2 was assessed with a paired-comparison familiarization-novelty paradigm. It was found that the addition of elements here significantly aided discrimination of linear segment orientation, but not curvilinear segment orientation. Experiment 3 investigated why this effect was not found for curvilinear segments; after equating the curvilinear stimuli to linear ones used in Experiment 2 with respect to the closedness of figure, discrimination of curvilinear orientation was observed.     

Stimulus averaging and the context for judgment

Loudness judgments of stimulus sets composed of four bursts of noise were analyzed for two types of contextual effects: between-set and within-set. Experiment I demonstrated between-set effects for these four-component stimuli; they were shown to be similar to those found in previous work with single stimuli. Experiment 2 tested an averaging model for within-set contextual effects. The results were inconsistent with the model. One interpretation is that there are within-set effects and that these are caused by shifts in the effective range of stimuli. Alternative interpretations attribute the apparent contextual effects either to an averaging of physical values or to an inappropriate scale of judgment.     

Stimulus generalization, context change, and forgetting

Forgetting is often attributed to retrieval failure caused by background contextual cues changing over time. However, generalization between stimuli may increase over time and make them increasingly interchangeable. If this effect occurs with contextual cues, it might cancel any effect of a changing context. The authors review the evidence and suggest a resolution of this paradox. Although generalization gradients can change over time, the effect is not always strong. Increased responding to nontarget stimuli is not often shown, and few studies have demonstrated such changes with contextual cues in a way that rules out other interpretations. Even this example of forgetting may be caused by retrieval failure. The physical contexts manipulated in learning and memory experiments themselves occur within a superordinate temporal context and can thus be forgotten with no inherent challenge to a context-change account of forgetting.     

Stimulus context and absolute magnitude estimation: a study of individual differences

The effect of stimulus context on absolute-magnitude-estimation (AME) judgments was examined by determining whether the loudness judgment of a tone is influenced by the intensities of other tones presented within the session. A group of 18 subjects was tested in separate sessions in which they judged stimuli within either a low (10-60 dB SL) or a high (40-90 dB SL) range of intensities. Examination of the results of individual subjects revealed that judgments of stimuli common to the two ranges were, in most subjects, unaffected or only slightly affected by the position of the range. The judgments of 2 subjects who failed to follow the instructions, however, showed very large context effects due to changing the stimulus range. The results of a second experiment, in which 22 subjects judged the loudness of tones within either a narrow (35-65 dB SL) or a wide (20-80 dB SL) range, revealed that, in all but 1 subject, the width of the range had no systematic effect on the loudness judgments of stimuli common to both ranges. This was also true 1 month later when 16 of the subjects returned to the laboratory to judge the loudness of tones within an even wider range of 10-90 dB SL. It was concluded that AME judgments are relatively insensitive to the potential biasing influences of stimulus context.     

Resistance to satiation: Reinforcing effects of food and eating under satiation

It has been shown previously that rats which have learned a response when hungry will continue to make that response when tested satiated, a phenomenon labeled resistance to satiation. Here we showed that rats which were previously trained hungry will learn a new response for the opportunity to consume pellets in a new situation when tested satiated. In four experiments various groups received each of the components of the training given when rats learn an instrumental response when hungry. Rats were placed in the goalbox of a straight alley and given food pellets when hungry or were hungry only in their home cages prior to running a straight alley in the satiated test in Experiment 1. In Experiments 2, 3, and 4 learning of a differential conditioning problem for pellets in S+ (nonreward in S?) was measured in the satiated test. Groups given pellets in their home cages when hungry with or without alley exposure learned to run more rapidly in S+ than in S? in the satiated test phase. The tendency to eat pellets in the apparatus and the reinforcing effect of eating the pellets was larger for rats which ate the pellets when hungry in their home cage than for rats which ate the pellets when satiated in their home cage. Being hungry in the home cage with no pellets was not sufficient to produce eating or running for pellets in the satiated test, indicating that any inherent reinforcing effect of the pellets is not sufficient to produce eating or running, and that incomplete satiation cannot account for the learning. These data indicate that a reinforcing effect of eating pellets under satiation is an important determiner of resistance to satiation.     

Vicarious goal satiation

A signature feature of self-regulation is that once a goal is satiated, it becomes deactivated, thereby allowing people to engage in new pursuits. The present experiments provide evidence for vicarious goal satiation, a novel phenomenon in which individuals experience “post-completion goal satiation” as a result of unwittingly taking on another person's goal pursuit and witnessing its completion. In Experiments 1 and 2, the observation of a goal being completed (vs. not completed) led to less striving by the observer on the same task. Given that an actor's strength of commitment affects goal contagion, we hypothesized that such commitment would be an important boundary condition for vicarious goal satiation. The results of Experiment 2 showed that observing stronger (vs. weaker) goal commitment lowered accessibility of goal-related words, but only when the goal being observed was completed. Implications of vicarious goal satiation for goal pursuit in everyday environments are discussed.     

On Stimulus Generalization and Stimulus Classes

Stimulus generalization has been defined as the spread of effect of reinforcement for responses emitted in the presence of one stimulus to different stimuli presented under extinction conditions. As a result of stimulus generalization, novel stimuli come to exert stimulus control over members of the response class. Studies in the applied behavior analysis literature, however, have reported experimental preparations that included prompting and reinforcement procedures during what were claimed to be stimulus generalization conditions. These studies violated the procedural requirement that stimulus generalization be tested under extinction conditions. Responses that come under the control of a class of stimuli may do so by direct training or by stimulus generalization. It is desirable for organisms to respond in the presence of members of an appropriately constructed stimulus class, but we should understand the mechanism of entry into the class by its members. If inaccurate claims of stimulus generalization are made when training procedures are used in the ostensible generalization conditions, the robustness of the original training procedures will be over estimated. By adhering to the operational requirements of behavioral definitions, we could better understand the power and limits of our educational and training procedures.     

Stimulus complexity effects in visual comparisons: the effects of practice and learning context.

This study examined visual comparison performance for 6-24-point random polygon stimuli (Cooper & Podgorny, 1976). Stimulus complexity effects decreased with practice, consistent with Bethell-Fox and Shepard (1988). A difficult discrimination context produced greater complexity effects than an easy discrimination context, consistent with Folk and Luce (1987). The difficult discrimination context also led to more stimulus-specific learning and diminished stimulus complexity effects. Increased stimulus learning resulted in continued skill acquisition, better transfer, and less performance disruption when the task context was equated for all Ss. It is argued that improvements in performance in a perceptual comparison task are not solely a function of the amount of practice provided in responding to particular stimuli. The context in which responses are elicited is equally important and must be accommodated in theories of skill acquisition.     

Semantic satiation and lexical ambiguity resolution.

This study examines the effects of semantic satiation on lexical ambiguity resolution. On a given trial, participants were presented with a word triad. The first word (e.g., HEART) was presented on average 2.5, 12.5, or 22.5 times, and then participants received 2 new words for relatedness judgments. The first of the two new words was always a homograph (e.g., "ORGAN") and the other word was a related or unrelated pairmate (e.g., "KIDNEY"). In Experiment 1, when blocks of trials were intermixed with concordant (e.g., "HEART-ORGAN-KIDNEY"), discordant (e.g., "PIANO-ORGAN-KIDNEY"), and neutral (e.g., "CEILING-ORGAN-KIDNEY") trials, participants did not produce evidence of semantic satiation. In a second experiment in which only concordant and neutral trials were presented, however, participants did produce evidence of semantic satiation in the concordant condition. Taken together, Experiments 1 and 2 indicate that semantic satiation of the context-appropriate meaning of a homograph may impede ambiguity resolution.     

Food satiation in the pigeon

The experiment was designed to find the shape of food satiation curves of the pigeon as a function of hours of deprivation or percentage of free-feeding weight, and to study the fluctuation in free-feeding weight as a function of deprivation and satiation. At a systematically and progressively increased number of hours'' deprivation, eight birds were allowed to satiate on grain presented contingent upon the emission of a pecking response. In the second part of the experiment, in which two birds were used, a similar procedure was followed except that the independent variable was percentage of free-feeding weight. These were the conclusions.1. Approximately 64% of the satiation curves were classified as straight with an abrupt stop. The next highest percentage of curves was 18% for curves classified as straight with a curvilinear stop. No “classic” satiation curves, curvilinear with curvilinear stop, were found.2. The pigeons responded at fairly constant rate during the early part of each satiation session, or they did not respond at all. The critical weight, above which they did not respond, was 85% of free feeding.