Tim Curran

Brain potentials of recollection and familiarity

It is widely hypothesized that separate recollection and familiarity processes contribute to recognition memory. The present research measured event-related brain potentials (ERPs) from 128 head locations to identify patterns of brain activity related to recollection and familiarity. In two experiments, subjects performed a recognition memory task requiring discrimination between previously studied words, similar words that changed plurality between study and test, and new words (following Hintzman & Curran, 1994). The FN400 ERP component (300–500 msec) varied with the familiarity of words (new>studied = similar). The parietal component (400–800 msec) was associated with the recollection of plurality (studied > similar = new). Differences in the timing and spatial topography of the FN400 and parietal effects support the view that familiarity and recollection arise from distinct neurocognitive processes.

Attentional and Nonattentional Forms of Sequence Learning

This research investigated the hypothesis that sequential patterns of behavior can be learned by 2 independent mechanisms. One requires attention to the relation between successive events, whereas the other operates independently of such attention. In 4 experiments, subjects learned visuospatial sequences in a serial reaction time task. The relation between attentional and nonattentional learning was explored by assessing the extent to which learning transferred between conditions with or without distraction. The results suggest that attentional and nonattentional learning operate independently, in parallel, do not share information, and represent sequential information in qualitatively different ways. A fundamental type of learning in which humans excel is the learning of sequential patterns of behavior. In four experiments, we investigated the hypothesis that humans exhibit two forms of sequential learning. One form of learning requires attention to the relation between successive events in the sequence, not only for acquisition but also for the expression of the learning in performance. We hypothesized that the other type of sequential learning did not require attention to these relations. Furthermore, these two forms of learning are independent of one another, with no communication or sharing of information between them. If subjects perform a series of behavioral acts that occur in a predictable order and under conditions relatively free of distraction, we suppose that attentionally based and nonattentionally based learning of the sequence occur in parallel. If distraction is added during learning, the attentional form is disabled, but the nonattentional one is unmodified. That is, attention is neither necessary nor helpful to the nonattentional form of learning. This hypothesis is similar to ideas examined by other investigators but is also different in several ways. Nissen and her colleagues (Nissen & Bullemer, 1987; Willingham, Nissen, & Bullemer, 1989; see also Lewicki, Hill, & Bizot, 1988; Stadler, 1989) have suggested that learning of sequences can be either procedural (without awareness) or declarative (with awareness). Both of these, according to Nissen, require attention. We distinguish both of those forms from a third, nonattentional type of learning.

A Neural Basis for Expert Object Recognition

Although most adults are considered to be experts in the identification of faces, fewer people specialize in the recognition of other objects, such as birds and dogs. In this research, the neurophysiological processes associated with expert bird and dog recognition were investigated using event-related potentials. An enhanced early negative component (N170, 164 ms) was found when bird and dog experts categorized objects in their domain of expertise relative to when they categorized objects outside their domain of expertise. This finding indicates that objects from well-learned categories are neurologically differentiated from objects from lesser-known categories at a relatively early stage of visual processing.

Striatal recruitment during an implicit sequence learning task as measured by functional magnetic resonance imaging

Prior research has repeatedly implicated the striatum in implicit sequence learning; however, imaging findings have been inconclusive with respect to the sub‐territories and laterality involved. Using functional magnetic resonance imaging (fMRI), we studied brain activation profiles associated with performance of the serial reaction time task (SRT) in 10 normal right‐handed males. Behavioral results indicate that significant implicit learning occurred, uncontaminated by significant explicit knowledge. Concatenated fMRI data from the entire cohort revealed significant right‐lateralized activation in both the caudate and putamen. Analysis of fMRI data from individual subjects showed inter‐individual variability as to the precise territories involved, including right as well as left caudate and putamen. Interestingly, all seven subjects who manifested robust learning effects exhibited significant activation within the putamen. Moreover, among those seven subjects, the magnitude of signal intensity change within the putamen correlated significantly with the magnitude of reaction time advantage achieved. These findings demonstrate right‐sided striatal activation across subjects during implicit sequence learning, but also highlight interindividual variability with respect to the laterality and striatal subterritories involved. In particular, results from individual subjects suggest that, during the SRT, the reaction time advantage garnered via implicit sequence learning might be predominantly associated with activity within the putamen. Hum. Brain Mapping 5:124–132, 1997.

Perceptual interference supports a non-modular account of face processing

The perception of faces and of nonface objects share common early visual processing stages. Some argue, however, that the brain eventually processes faces separately from other objects, within a domain-specific module dedicated to face perception. This apparent specialization for faces could, alternatively, result from peoples expertise with this category of stimuli. Here we used behavioral and electrophysiological measures of interference to address the functional independence of face and object processing. If the expert processing of faces and cars depend on common mechanisms related to holistic perception (obligatory processing of all parts), then for human subjects who are presumed to be face experts, car perception should interfere with concurrent face perception. Furthermore, such interference should increase with greater expertise in car identification, and indeed this is what we found. Event-related potentials (ERPs) suggest that this interference arose from perceptual processes contributing to the holistic processing of both objects of expertise and faces.

Error-Related Negativity Predicts Reinforcement Learning and Conflict Biases

The error-related negativity (ERN) is an electrophysiological marker thought to reflect changes in dopamine when participants make errors in cognitive tasks. Our computational model further predicts that larger ERNs should be associated with better learning to avoid maladaptive responses. Here we show that participants who avoided negative events had larger ERNs than those who were biased to learn more from positive outcomes. We also tested for effects of response conflict on ERN magnitude. While there was no overall effect of conflict, positive learners had larger ERNs when having to choose among two good options (win/win decisions) compared with two bad options (lose/lose decisions), whereas negative learners exhibited the opposite pattern. These results demonstrate that the ERN predicts the degree to which participants are biased to learn more from their mistakes than their correct choices and clarify the extent to which it indexes decision conflict.

Neuroanatomical Correlates of Veridical and Illusory Recognition Memory: Evidence from Positron Emission Tomography

Memory distortions and illusions have been thoroughly documented in psychological studies, but little is known about the neuroanatomical correlates of true and false memories. Vivid but illusory memories can be induced by asking people whether they recall or recognize words that were not previously presented, but are semantically related to other previously presented words. We used positron emission tomography to compare brain regions involved in veridical recognition of printed words that were heard several minutes earlier and illusory recognition of printed words that had not been heard earlier. Veridical and illusory recognition were each associated with blood flow increases in a left medial temporal region previously implicated in episodic memory; veridical recognition was distinguished by additional blood flow increases in a left temporoparietal region previously implicated in the retention of auditory/phonological information. This study reveals similarities and differences in the way the brain processes accurate and illusory memories.

FALSE RECOGNITION AND THE RIGHT FRONTAL LOBE : A CASE STUDY

We described a patient, BG, who exhibited a striking pattern of false recognition after an infarction of the right frontal lobe. Seven experiments document the existence of the phenomenon, explore its characteristics, and demonstrate how it can be eliminated. BG showed pathologically high false alarm rates when stimuli were visual words (experiments 1 and 4), auditory words (experiment 2), environmental sounds (experiment 3), pseudowords (experiment 5), and pictures (experiment 7). His false alarms were not merely attributable to the semantic or physical similarity of studied and non-studied items (experiments 4 and 5). However, BGs false recognitions were virtually eliminated by presenting him with categorized stimuli and testing him with new stimuli from non-studied categories (experiments 6 and 7). The results suggest that BGs false alarms may be attributable to an over-reliance on memory for general characteristics of the study episode, along with impaired memory for specific items. The damaged right frontal lobe mechanisms may normally support the monitoring and/or retrieval processes that are necessary for item-specific recognition.

Using ERPs to dissociate recollection from familiarity in picture recognition

Dual process theories posit that separate recollection and familiarity processes contribute to recognition memory. Previous research, testing recognition memory for words, indicates that event-related brain potentials (ERPs) can be used to dissociate recollection from familiarity. It has been hypothesized that the FN400 ERP old/new effect (300-500 ms) varies with stimulus familiarity, but the parietal ERP old/new effect (400-800 ms) varies with recollection. The results reported here are consistent with this hypothesis, extending it to the recognition of pictures when subjects had to discriminate between studied pictures, highly familiar lures (mirror-reversals of studied pictures), and new pictures. Furthermore, the parietal old/new effect showed significant recollection-related differences only for subjects with good behavioral discrimination between studied items and similar lures.

Activation of Preexisting and Acquired Face Representations: The N250 Event-related Potential as an Index of Face Familiarity

Electrophysiological studies using event-related potentials have demonstrated that face stimuli elicit a greater negative brain potential in right posterior recording sites 170 msec after stimulus onset (N170) relative to nonface stimuli. Results from repetition priming paradigms have shown that repeated exposures of familiar faces elicit a larger negative brainwave (N250r) at inferior temporal sites compared to repetitions of unfamiliar faces. However, less is known about the time course and learning conditions under which the N250 face representation is acquired. In the familiarization phase of the Joe/no Joe task, subjects studied a target Joe face (Jane for female subjects) and, during the course of the experiment, identified a series of sequentially presented faces as either Joe or not Joe. The critical stimulus conditions included the subjects own face, a same-sex Joe ( Jane) face and a same-sex other face. The main finding was that the subjects own face produced a focal negative deflection (N250) in posterior channels relative to nontarget faces. The task-relevant Joe target face was not differentiated from other nontarget faces in the first half of the experiment. However, in the second half, the Joe face produced an N250 response that was similar in magnitude to the own face. These findings suggest that the N250 indexes two types of face memories: a preexperimentally familiar face representation (i.e., the own face and a newly acquired face representation (i.e., the Joe/Jane face) that was formed during the course of the experiment.