Robert D. Melara

P2 enhancement from auditory discrimination training is associated with improved reaction times

This study examined the effects of training in a pure tone discrimination task on relations between behavioral performance and the magnitude of auditory event-related potentials (ERPs). Participants performed both passive (listening) and active (detecting) oddball tasks in a pretest and two posttests (1 and 9 weeks after training). Training produced a long-term benefit in both perceptual sensitivity and reaction times (RT). Training enhanced the amplitude of the P2 ERP component to both standards and deviants at both early and delayed posttests. Importantly, P2 enhancement was strongly associated with discrimination RT, suggesting that experience facilitates rapid, preattentive access to perceptual representations. Training also elevated the mismatch negativity, possibly due to the strengthening of acoustic traces. Finally, training enhanced the amplitude of the P3 component to deviants across posttests, indicating a long-lasting effect of discrimination training on stimulus salience.

Sequential effects in the Simon task: Conflict adaptation or feature integration?

Sequential effects--reduced behavioral interference after incongruent trials-provide a unique opportunity to examine the influence of previous experience on current attentional processing. We conducted a theoretical analysis of performance in the Simon paradigm to distinguish an attention account (conflict adaptation) from a working memory account (feature integration). Results supported the memory account. Feature unbinding contributed significantly to sequential effects, even when separated statistically from the effects of Simon conflict. Sequential effects to neutral stimuli were comparable to those found with Simon stimuli, suggesting at most a minor contribution from conflict adaptation. These patterns emerged in behavioral data (reaction time and accuracy) and in two event-related potential components: N2 and SP (a slow positivity 480-520 ms after stimulus onset). They suggest that sequential effects arise from the partial mismatch of S-R features in working memory.

Electrophysiological evidence for early interaction between talker and linguistic information during speech perception

This study combined behavioral and electrophysiological measurements to investigate interactions during speech perception between native phonemes and talkers voice. In a Garner selective attention task, participants either classified each sound as one of two native vowels ([epsilon] and [ae]), ignoring the talker, or as one of two male talkers, ignoring the vowel. The dimension to be ignored was held constant in baseline tasks and changed randomly across trials in filtering tasks. Irrelevant variation in talker produced as much filtering interference (i.e., poorer performance in filtering relative to baseline) in classifying vowels as vice versa, suggesting that the two dimensions strongly interact. Event-related potentials (ERPs) were recorded to identify the processing origin of the interference: an early disruption in extracting dimension-specific information or a later disruption in selecting appropriate responses. Processing in the filtering task was characterized by a sustained negativity starting 100 ms after stimulus onset and peaking 200 ms later. The early onset of this negativity suggests that interference originates in the cognitive effort required by listeners to extract dimension-specific information, a process that precedes response selection. In agreement with these findings, our results revealed numerous dimension-specific effects, most prominently in the filtering tasks.

Attentional origins of the Simon effect : Behavioral and electrophysiological evidence

An electrophysiological analysis of classification in the Garner paradigm was performed to investigate processing origins of the Simon effect. This effect is faster responding when stimulus location, though irrelevant to the task, is congruent with the response to the relevant stimulus dimension than when it is not. Participants used lateral keys to classify the timbre of tones presented to left or right headphones. Differences between S-R congruent and S-R incongruent trials were observed initially in the N2 ERP component (250 ms after stimulus onset), after the N1 component (100 ms after stimulus onset) showed evidence of a failure of selective attention to stimulus location. Reaction times to congruent and incongruent stimuli were strongly associated with the peak latency of the P3 decisional component. The results are consistent with models that attribute the Simon effect to the evidentiary weight attention assigns to spatial location when classifying the stimulus as signaling left or right.

Control of working memory: effects of attention training on target recognition and distractor salience in an auditory selection task.

Behavioral and electrophysiological measures of target and distractor processing were examined in an auditory selective attention task before and after three weeks of distractor suppression training. Behaviorally, training improved target recognition and led to less conservative and more rapid responding. Training also effectively shortened the temporal distance between distractors and targets needed to achieve a fixed level of target sensitivity. The effects of training on event-related potentials were restricted to the distracting stimulus: earlier N1 latency, enhanced P2 amplitude, and weakened P3 amplitude. Nevertheless, as distractor P2 amplitude increased, so too did target P3 amplitude, connecting experience-dependent changes in distractor processing with greater distinctiveness of targets in working memory. We consider the effects of attention training on the processing priorities, representational noise, and inhibitory processes operating in working memory.

Behavioral and electrophysiological effects of distractor variation on auditory selective attention.

Two experiments investigated the effects on auditory selection of varying distractor values in memory. Participants performed a set of control (single distractor) and distractor-variation (multiple distractors) tasks, classifying targets by pitch (Experiments 1A and 2) or loudness (Experiment 1B) while ignoring previously presented (and spatially separate) distractors. When both targets and distractors varied in pitch, the degree of variation among the distractors increasingly disrupted classification accuracy and reaction time to the targets. Physiologically, the degree of distractor variation boosted the N1 response to distractors, the P2 response to both targets and distractors, and the slow-wave response to targets (400-600 ms after stimulus onset). The results suggest that target representations are diminished in distinctiveness as distractors activate a wider range of the task-relevant continuum in working memory.

Can Children With SLI Detect Cognitive Conflict? Behavioral and Electrophysiological Evidence

PURPOSE This study examined whether children with specific language impairment (SLI) are deficient in detecting cognitive conflict between competing response tendencies in a GO/No-GO task. METHOD Twelve children with SLI (ages 10-12), 22 children with typical language development matched group-wise on age (TLD-A), and 16 younger children with TLD (ages 8-9) matched group-wise on language skills (TLD-L) were tested using a behavioral GO/No-GO paradigm with simultaneous collection of event-related potentials. The N2 component was used as a neural index of the ability to detect conflict between GO and No-GO response tendencies. RESULTS Hit rates did not differentiate the 3 groups. The TLD-L children demonstrated the highest false-alarm rates. The N2 component was attenuated and showed delayed divergence of GO and No-GO amplitudes in SLI relative to TLD-A children in response to stimuli presented at various probability levels. The N2 effect in children with SLI resembled that of children with TLD who were approximately 3 years younger. CONCLUSIONS School-age children with SLI exhibit a maturational lag in detecting conflict between competing response alternatives. Deficient conflict detection may in turn hinder these childrens ability to resolve conflict among semantic representations that are activated during language processing.

Rejection positivity predicts trial-to-trial reaction times in an auditory selective attention task: a computational analysis of inhibitory control

A series of computer simulations using variants of a formal model of attention (Melara and Algom, 2003) probed the role of rejection positivity (RP), a slow-wave electroencephalographic (EEG) component, in the inhibitory control of distraction. Behavioral and EEG data were recorded as participants performed auditory selective attention tasks. Simulations that modulated processes of distractor inhibition accounted well for reaction-time (RT) performance, whereas those that modulated target excitation did not. A model that incorporated RP from actual EEG recordings in estimating distractor inhibition was superior in predicting changes in RT as a function of distractor salience across conditions. A model that additionally incorporated momentary fluctuations in EEG as the source of trial-to-trial variation in performance precisely predicted individual RTs within each condition. The results lend support to the linking proposition that RP controls the speed of responding to targets through the inhibitory control of distractors.

Does Working Memory Enhance or Interfere With Speech Fluency in Adults Who Do and Do Not Stutter? Evidence From a Dual-Task Paradigm

PURPOSE The present study examined whether engaging working memory in a secondary task benefits speech fluency. Effects of dual-task conditions on speech fluency, rate, and errors were examined with respect to predictions derived from three related theoretical accounts of disfluencies. METHOD Nineteen adults who stutter and twenty adults who do not stutter participated in the study. All participants completed 2 baseline tasks: a continuous-speaking task and a working-memory (WM) task involving manipulations of domain, load, and interstimulus interval. In the dual-task portion of the experiment, participants simultaneously performed the speaking task with each unique combination of WM conditions. RESULTS All speakers showed similar fluency benefits and decrements in WM accuracy as a result of dual-task conditions. Fluency effects were specific to atypical forms of disfluency and were comparable across WM-task manipulations. Changes in fluency were accompanied by reductions in speaking rate but not by corresponding changes in overt errors. CONCLUSIONS Findings suggest that WM contributes to disfluencies regardless of stuttering status and that engaging WM resources while speaking enhances fluency. Further research is needed to verify the cognitive mechanism involved in this effect and to determine how these findings can best inform clinical intervention.

Facial trustworthiness perception bias elevated in individuals with PTSD compared to trauma exposed controls

Posttraumatic stress disorder (PTSD) research has focused largely on fear processing. However, interpersonal trauma exposure can also impact interpersonal functioning and the perception of the trustworthiness of others. The present study examined facial perceptions of fearfulness and trustworthiness in individuals with PTSD (n=29), trauma-exposed without PTSD (n=19), and healthy controls (n=18). The PTSD group was hypothesized to exhibit a bias to perceive more fear and untrustworthiness in faces relative to controls. Participants rated the level of fearfulness or trustworthiness of faces that were parametrically morphed along a fear or trustworthiness dimension. The PTSD group was biased to perceive faces as more trustworthy compared to the trauma-exposed healthy controls, yet there were no differences between groups in fear processing. A trustworthiness bias in PTSD may represent a vulnerability factor. Conversely, lower trustworthiness perception may represent a protective disposition in trauma-exposed individuals who do not develop PTSD. Differences in the perception of trustworthiness may be an aspect of social perception that is independent of the fear processing abnormalities observed in PTSD.