Failure to Produce False Memories Through the Stimulus Equivalence Paradigm

Stimulus equivalence has been adopted as a behavioral explanation for false memories. The present study aimed to test false memories using lists compound of equivalent stimuli. 10 undergraduate students learned three 4-member (Classes 1, 2, 3) and three 12-member equivalence classes (Classes 4, 5, 6). A week later these participants performed a recognition test. Participants first saw a study list comprising 10 of the 12 stimuli from Classes 4, 5 and 6. Later, they saw a list comprising all stimuli from study list (targets), the remaining stimuli from the Classes 4, 5 and 6 (critical lures) and nine stimuli from Classes 1, 2 and 3 (non-related lures). Due to the equivalence relation between targets and critical lure, it was expected that the second would be recognize as much as the first, but results indicated critical and non-related lures where equally recognized and at low levels.

Incongruent Abstract Stimulus–Response Bindings Result in Response Interference: fMRI and EEG Evidence from Visual Object Classification Priming

Stimulus repetition often leads to facilitated processing, resulting in neural decreases (repetition suppression) and faster RTs (repetition priming). Such repetition-related effects have been attributed to the facilitation of repeated cognitive processes and/or the retrieval of previously encoded stimulus–response (S-R) bindings. Although previous research has dissociated these two forms of learning, their interaction in the brain is not fully understood. Utilizing the spatial and temporal resolutions of fMRI and EEG, respectively, we examined a long-lag classification priming paradigm that required response repetitions or reversals at multiple levels of response representation. We found a repetition effect in occipital/temporal cortex (fMRI) that was time-locked to stimulus onset (EEG) and robust to switches in response, together with a repetition effect in inferior pFC (fMRI) that was time-locked to response onset (EEG) and sensitive to switches in response. The response-sensitive effect occurred even when changing from object names (words) to object pictures between repetitions, suggesting that S-R bindings can code abstract representations of stimuli. Most importantly, we found evidence for interference effects when incongruent S-R bindings were retrieved, with increased neural activity in inferior pFC, demonstrating that retrieval of S-R bindings can result in facilitation or interference, depending on the congruency of response between repetitions.

Abstract Stimulus-Specific Adaptation Models

Many neurons that initially respond to a stimulus stop responding if the stimulus is presented repeatedly but recover their response if a different stimulus is presented. This phenomenon is referred to as stimulus-specific adaptation (SSA). SSA has been investigated extensively using oddball experiments, which measure the responses of a neuron to sequences of stimuli. Neurons that exhibit SSA respond less vigorously to common stimuli, and the metric typically used to quantify this difference is the SSA index (SI). This article presents the first detailed analysis of the SI metric by examining the question: How should a system (e.g., a neuron) respond to stochastic input if it is to maximize the SI of its output? Questions like this one are particularly relevant to those wishing to construct computational models of SSA. If an artificial neural network receives stimulus information at a particular rate and must respond within a fixed time, what is the highest SI one can reasonably expect? We demonstrate that the optimum, average SI is constrained by the information in the input source, the length and encoding of the memory, and the assumptions concerning how the task is decomposed.

On Knowing Books by Their Colors

In a search and recognition task utilizing real-world objects, the usefulness of color cues is observed to depend upon the availability of alphanumeric information. Following a 45-sec. inspection of a randomly selected collection of 17 books, spread on a table with their titles exposed, subjects were asked to identify as many of these as possible during a test period beginning 3 min. later in which 17 decoys were also present. Some subjects wore glasses with red filters during the test and inspection periods. The color blindness thereby introduced did not impair their performance in comparison with control subjects who were able to utilize normal color vision. Moreover, the introduction of color during the test period impaired the performance of subjects who had been deprived of color cues during inspection. It was concluded that subjects paid attention mostly to book titles and for that reason did not use other cues, including color, to much advantage. In a second experiment, where titles were obscured, subjects with normal color vision performed much better than those who were made color blind during the inspection or test periods. The results of both experiments are generally consistent with predictions based on experiments which have used abstract stimulus materials.

Picture Mediation in Abstract-Concrete Paired Associates

The present study investigated the hypothesis that pictures of abstract-concrete paired associates would serve to make the abstract stimulus member more concrete thereby enhancing the learning process. 60 subjects were equally divided into 6 groups, varying conditions of concreteness and abstractness of the stimulus items and pictures or no picture. The results supported the basic proposition that the picture mediation presented during the learning-testing condition facilitated the learning of the abstract paired associates.