Continuous Recognition Task Research Articles

Recollection Training and Transfer Effects in Older Adults: Successful Use of a Repetition-Lag Procedure

We examined an approach aimed at training consciously-controlled recollection, introduced by Jennings and Jacoby (2003), for its ability to replicate and generalize. A continuous recognition task, requiring recollection to identify the occurrence of repeated items over gradually increasing lag intervals (number of intervening items between the first and second presentation of a repeated word), was given to a group of older adults twice a week for three weeks. Pre-and-post training performance was assessed on multiple measures and compared with a recognition practice and no contact control group. Recollection training proved successful; accurate identification of repeated items increased across a lag interval of 2 to 18 intervening items. Post-training gains following recollection training were found on n-back, self-ordered pointing, source discrimination and digit symbol substitution, but not with reading span or the CVLT-II. No changes were identified in the other groups. Gains from recollection training seem to transfer successfully in older adults.

Reproducibility of measures of neurophysiological activity in Wernicke's area: A magnetic source imaging study

Objective The purpose of this study was to evaluate the reproducibility of estimates of neurophysiological activity obtained with Magnetic Source Imaging. Methods Split-half data sets were obtained from 14 healthy volunteers during performance of a continuous recognition task for spoken words. The concurrent validity of spatiotemporal activation maps obtained with this task has been previously verified through comparisons with the Wada test and electrocortical stimulation mapping. Consecutive late activity sources (>200 ms after stimulus onset) were modeled independently as equivalent current dipoles (ECDs) and used to identify the location of language-specific cortex in the left hemisphere (Wernicke's area). Results Linear displacement of the geometric center of the cluster of ECDs in this region ranged between 2 and 8 mm across subjects. Intraparticipant variability (range) in the onset latency of activity was ±50 ms, while the range of change in global field power for the entire set of ECDs in Wernicke's area was less than 17% in all cases. Conclusions The results indicate that despite its many conceptual limitations the ECD model can provide reliable estimates of regional cortical activity associated with the engagement of linguistic processes. Significance The results highlight the need for reproducibility studies when research questions pose particular requirements for precision of estimates of regional neurophysiological activity.

Implicit and explicit memory in patients with obsessive-compulsive disorder: An event-related potential study

The implicit and explicit memory in patients with obsessive-compulsive disorder (OCD) was investigated using the event-related potential (ERP). For the assessment of implicit memory, a lexical decision task was administered. Among a total of 320 words and 140 non-words, 200 words were repeated, while the remaining 120 words and the 140 non-words were not repeated. For explicit memory, a continuous recognition task was administered, in which 280 words were repeated and 100 were not repeated. On the recognition task, both the controls and OCD patients showed more positivity to the old words than to the new words during the 200–600 ms period post-stimulus. Both groups showed faster response time to the old words than to the new words. On the lexical decision task, the controls showed the old/new effect during the 200–500 ms period post-stimulus, while the OCD patients did not. However, OCD patient showed faster response time to the old words than to the new words, although OCD patients showed prolonged response times to the old words compared to the controls. These results indicate that OCD patients have preserved explicit and implicit memory. The absence of old/new effect on ERP in OCD patients was discussed in terms of dysfunction of frontostriatal system, which plays an important role in both OCD and implicit memory.

Effects of baseline task position on apparent activation in functional imaging of memory

Brain activation dissociates during the repeated performance of memory tasks with decreasing medial temporal and increasing orbitofrontal activation. The impact of such adaptations on a baseline task is unknown. In this study, we used H 2 15O positron emission tomography (PET) in two groups of subjects performing a continuous recognition task and a baseline task. The group performing the baseline task after the main task showed significant medial temporal activation in the subtraction (recognition task–baseline). The group performing the baseline task at the beginning showed right orbitofrontal activation. These differences appeared to result primarily from different activations during the baseline task. It thus appears that the temporal context of a baseline task may fundamentally alter cognitive requirements and substantially influence apparent brain activation during a memory task. We suggest that the automatic filtration of memories according to their relevance for ongoing reality, a capacity mediated by the orbitofrontal cortex, is one such influence on apparent activation.

The brain uses single-trial multisensory memories to discriminate without awareness

Multisensory experiences enhance perceptions and facilitate memory retrieval processes, even when only unisensory information is available for accessing such memories. Using fMRI, we identified human brain regions involved in discriminating visual stimuli according to past multisensory vs. unisensory experiences. Subjects performed a completely orthogonal task, discriminating repeated from initial image presentations intermixed within a continuous recognition task. Half of initial presentations were multisensory, and all repetitions were exclusively visual. Despite only single-trial exposures to initial image presentations, accuracy in indicating image repetitions was significantly improved by past auditory–visual multisensory experiences over images only encountered visually. Similarly, regions within the lateral–occipital complex–areas typically associated with visual object recognition processes–were more active to visual stimuli with multisensory than unisensory pasts. Additional differential responses were observed in the anterior cingulate and frontal cortices. Multisensory experiences are registered by the brain even when of no immediate behavioral relevance and can be used to categorize memories. These data reveal the functional efficacy of multisensory processing.

Oscillatory EEG Correlates of Episodic Trace Decay

Recent studies suggest that human theta oscillations appear to be functionally associated with memory processes. It is less clear, however, to what type of memory sub-processes theta is related. Using a continuous word recognition task with different repetition lags, we investigate whether theta reflects the strength of an episodic memory trace or general processing demands, such as task difficulty. The results favor the episodic trace decay hypothesis and show that during the access of an episodic trace in a time window of approximately 200-400 ms, theta power decreases with increasing lag (between the first and second presentation of an item). LORETA source localization of this early theta lag effect indicates that parietal regions are involved in episodic trace processing, whereas right frontal regions may guide the process of retrieval. We conclude that episodic encoding can be characterized by two different stages: traces are first processed at parietal sites at approximately 300 ms, then further processing takes place in regions of the medial temporal lobe at approximately 500 ms. Only the first stage is related to theta, whereas the second is reflected by a slow wave with a frequency of approximately 2.5 Hz.

Auditory hallucinations: Failure to inhibit irrelevant memories

Introduction. The frequency of auditory hallucinations (AH) is associated with efficiency in inhibiting irrelevant memories, suggesting that the presence of AH may be related to the intrusion of strongly activated representations in memory. Therefore, we hypothesised that the inability to suppress irrelevant memories would be found only in patients currently experiencing AH. Method. Performance on a repeated, continuous recognition task was examined in 23 schizophrenia patients with AH present, 20 schizophrenia patients with AH absent, and 24 healthy controls. Results. Patients with current AH made significantly more inappropriate responses (false alarms) to distractors seen on previous runs of the task than nonhallucinating patients. The ability to detect targets (hits) was significantly better in healthy controls than schizophrenia patients, however, there was no significant difference between the two patient subgroups. Conclusions. The findings confirm that the presence of AH involves a failure to suppress memories that are not relevant to ongoing reality. We propose that a combination of deficits in inhibition and (episodic) memory provides a useful model of AH, which can accommodate many of the characteristic features of the symptom and fits well with the neuroanatomical circuitry that is believed to underlie the occurrence of AH.

The role of multisensory memories in unisensory object discrimination

Past multisensory experiences can influence current unisensory processing and memory performance. Repeated images are better discriminated if initially presented as auditory–visual pairs, rather than only visually. An experience's context thus plays a role in how well repetitions of certain aspects are later recognized. Here, we investigated factors during the initial multisensory experience that are essential for generating improved memory performance. Subjects discriminated repeated versus initial image presentations intermixed within a continuous recognition task. Half of initial presentations were multisensory, and all repetitions were only visual. Experiment 1 examined whether purely episodic multisensory information suffices for enhancing later discrimination performance by pairing visual objects with either tones or vibrations. We could therefore also assess whether effects can be elicited with different sensory pairings. Experiment 2 examined semantic context by manipulating the congruence between auditory and visual object stimuli within blocks of trials. Relative to images only encountered visually, accuracy in discriminating image repetitions was significantly impaired by auditory–visual, yet unaffected by somatosensory–visual multisensory memory traces. By contrast, this accuracy was selectively enhanced for visual stimuli with semantically congruent multisensory pasts and unchanged for those with semantically incongruent multisensory pasts. The collective results reveal opposing effects of purely episodic versus semantic information from auditory–visual multisensory events. Nonetheless, both types of multisensory memory traces are accessible for processing incoming stimuli and indeed result in distinct visual object processing, leading to either impaired or enhanced performance relative to unisensory memory traces. We discuss these results as supporting a model of object-based multisensory interactions.

Word imageability affects the hippocampus in recognition memory

Concrete words, whose meanings are readily imagined, are better remembered than abstract words. However, the neural correlates of this effect are poorly understood. Here, we investigated the effect of imageability on brain activity in the medial temporal lobe (MTL) processes underlying recognition memory. We recorded event-related potentials (ERPs) via depth electrodes from within the MTL in 14 patients with drug-resistant epilepsy. Patients performed a continuous word recognition task with words of high and low imageability (controlled for word frequency). Behaviorally, recognition performance was better for high, compared to low, imageable words. Two ERP components associated with recognition memory, the AMTL-N400 and the hippocampal late negative component, showed an old/new effect, but only the hippocampal P600 showed a main effect of imageability. We suggest that the hippocampal effect of imageability in recognition memory may be associated with conceptual or pictorial information processing of concrete words.

Impairment of recognition memory in schizophrenia: event-related potential study using a continuous recognition task.

Recognition memory and the dissociation of immediate and delayed repetition in schizophrenic patients were investigated using event-related potential (ERP) and a continuous word recognition task. In total, 14 schizophrenic patients and 14 age and gender-matched control subjects, were recruited. Among 240 stimulus words used, 40 words were not repeated, 100 were repeated immediately, and 100 were repeated after five intervening words. Both schizophrenic and control groups responded faster to words repeated immediately than to words repeated after a delay and to new words. However, schizophrenic patients responded less accurately to words repeated immediately and to words repeated after a delay than the controls. In terms of ERP, schizophrenic patients showed significantly reduced N200, late positive component (LPC), and N400 amplitudes, and a more frontally-distributed N200 topography than the controls. For controls, immediate repetition was associated with a large LPC amplitude and the absence of N400, while delayed repetition was associated with a small LPC amplitude and the presence of N400. However, this dissociation between immediate and delayed repetition was not observed in schizophrenic patients. All of these results suggest that schizophrenic patients have recognition memory impairment, the cause of which may range from early encoding, and memory search to late retrieval.

Event-related potentials to unfamiliar faces in a recognition memory task

The purpose of this study was to investigate electrophysiological correlates related to the recognition of repeated faces in the intact human by means of event-related potentials (ERPs). Twenty young healthy adults (mean, 24.5 years) performed a continuous face recognition task, in which unfamiliar faces were flashed upon a computer screen. Some faces were repeated immediately after initial presentation (at lag 0), while others were repeated after one intervening face (at lag 1) or at lag 3. Subjects were requested to push a button with the right thumb upon first presentation of a face and with a left thumb upon repeat presentation. Significant differences were seen in accuracy of new/old responses between at lag 0 and at lags 1 or 3. Reaction time (RT) for faces repeated at lag 0 was significantly shorter than that for first (new) presentations. RT at lag 3, however, was longer than RT for new faces. The ERPs recorded from 7 scalp sites revealed more positive going waveforms beginning at about 200 ms (old/new effect) for the correctly classified repeated faces. The ERP old/new effects were more marked in anterior sites and were more prominent at lag 0 than at lags 1 and 3. It is thus concluded that the ERP old/new effect is demonstrated to unfamiliar faces and varies with repetition interval and scalp regions. In addition, some discrepancy was found between electrophysiological and behavioral priming effects.

Detection of Repeated Trigrams: Evidence of All-or-None Learning

Two experiments investigated trigram detection in a continuous recognition task. In Experiment 1 consonant trigrams were presented visually, one at a time, with occasional repetition of a trigram after an interval of 0, 2, 4, 8, or 16 other trigrams. Subjects were told to respond with a button press every time they saw a repeated trigram. If a subject responded to a repeated trigram, it was not repeated again. However, if a subject did not respond to a repeated trigram, it was repeated again at the same interval for up to 3 repetitions. For all intervals greater than 0, the probability of noticing a repeated trigram did not increase with the number of repetitions. In Experiment 2 meaningless shape trigrams were presented, and occasionally a trigram was repeated after an interval of 0, 1, or 2 trigrams. For both intervals greater than 0, the probability of noticing a repeated trigram did not increase with the number of repetitions. The results demonstrate that a repeated input does not necessarily leave a permanent trace in memory.

Continuous audio–visual digit recognition using N-best decision fusion

Audio–visual speech recognition systems can be categorised into systems that integrate audio–visual features before decisions are made (feature fusion) and those that integrate decisions of separate recognisers for each modality (decision fusion). Decision fusion has been applied at the level of individual analysis time frames, phone segments and for isolated word recognition but in its basic form cannot be used for continuous speech recognition because of the combinatorial explosion of possible word string hypotheses that have to be evaluated. We present a case for decision fusion at the utterance level and propose an algorithm that can be applied efficiently to continuous speech recognition tasks, which we call N -best decision fusion. The system was tested on a single-speaker, continuous digit recognition task where the audio stream was contaminated by additive multi-speaker babble noise. The audio–visual recognition system resulted in lower word error rates for all signal-to-noise conditions tested compared to the audio-alone system. The magnitude of the improvement was dependent on the signal-to-noise ratio.

Rapid discrimination of visual and multisensory memories revealed by electrical neuroimaging

Though commonly held that multisensory experiences enrich our memories and that memories influence ongoing sensory processes, their neural mechanisms remain unresolved. Here, electrical neuroimaging shows that auditory–visual multisensory experiences alter subsequent processing of unisensory visual stimuli during the same block of trials at early stages poststimulus onset and within visual object recognition areas. We show this with a stepwise analysis of scalp-recorded event-related potentials (ERPs) that statistically tested (1) ERP morphology and amplitude, (2) global electric field power, (3) topographic stability of and changes in the electric field configuration, and (4) intracranial distributed linear source estimations. Subjects performed a continuous recognition task, discriminating repeated vs. initial image presentations. Corresponding, but task-irrelevant, sounds accompanied half of the initial presentations during a given block of trials. On repeated presentations within a block of trials, only images appeared, yielding two situations—the image's prior presentation was only visual or with a sound. Image repetitions that had been accompanied by sounds yielded improved memory performance accuracy (old or new discrimination) and were differentiated as early as ∼ 60–136 ms from images that had not been accompanied by sounds through generator changes in areas of the right lateral–occipital complex (LOC). It thus appears that unisensory percepts trigger multisensory representations associated with them. The collective data support the hypothesis that perceptual or memory traces for multisensory auditory–visual events involve a distinct cortical network that is rapidly activated by subsequent repetition of just the unisensory visual component.

Improving memory in older adults: Training recollection

We explore a novel theory‐guided approach for training memory in older adults that distinguishes between recollection and automatic influences. Participants were given multiple trials of a continuous recognition task in which they had to use recollection to identify repeated items. After each correct trial, the number of intervening items between repetitions was gradually increased (incremented‐difficulty approach). Initially, accurate identification only occurred with two intervening items, which increased to 28 items following 6 hours of training. A second group of participants was given an equal amount of practice with the task but the number of intervening items was varied randomly across trials, independent of accuracy. These individuals showed significantly smaller gains in recollection. Results suggest that an incremented‐difficulty approach can enhance the ability to recollect information across increasing delay intervals. Implications for future training efforts are discussed.

Recognition memory for unfamiliar faces does not differ for adult normal and dyslexic readers: an event-related brain potential study.

Differences in recognition memory for unfamiliar faces between adult developmental dyslexic (n=12) and normal readers (n=12) were studied by means of event-related brain potentials. Subjects performed a continuous face recognition task, in which 240 unfamiliar faces were presented on a computer screen, 100 of which were repetitions. For each face, subjects had to indicate whether it was presented before or not. Performance did not differ between normal and dyslexic readers. Old/repeated faces elicited more positive event-related potentials (ERPs) starting 250 ms poststimulus. These were analyzed in two time-windows encompassing the early (250-450 ms) and the late phase (450-750 ms) of the old/new effect. No group difference in amplitude or topography of the old/new effect emerged. However, ERPs for all faces were more positive for normal compared with those of dyslexic readers. These results show that a previously described recognition memory deficit for words in dyslexic readers is likely to be specific for verbal material.

Conjunction error rates on a continuous recognition memory test: Little evidence for recollection.

Two experiments examined conjunction memory errors on a continuous recognition task where the lag between parent words (e.g., blackmail, jailbird) and later conjunction lures (blackbird) was manipulated. In Experiment 1, contrary to expectations, the conjunction error rate was highest at the shortest lag (1 word) and decreased as the lag increased. In Experiment 2 the conjunction error rate increased significantly from a 0- to a 1-word lag, then decreased slightly from a 1- to a 5-word lag. The results provide mixed support for simple familiarity and dual-process accounts of recognition. Paradoxically, searching for an item in memory does not appear to be a good encoding task.

Conjunction error rates on a continuous recognition memory test: Little evidence for recollection.

Two experiments examined conjunction memory errors on a continuous recognition task where the lag between parent words (e.g., blackmail, jailbird) and later conjunction lures (blackbird) was manipulated. In Experiment 1, contrary to expectations, the conjunction error rate was highest at the shortest lag (1 word) and decreased as the lag increased. In Experiment 2 the conjunction error rate increased significantly from a 0- to a 1-word lag, then decreased slightly from a 1- to a 5-word lag. The results provide mixed support for simple familiarity and dual-process accounts of recognition. Paradoxically, searching for an item in memory does not appear to be a good encoding task.

Encoding and retrieval related cerebral activation in continuous verbal recognition

The differential neuronal activation related to encoding of novel and recognition of previously studied items and the effect of retrieval effort on neuronal activation were assessed in a event-related functional magnetic resonance imaging experiment. A verbal continuous recognition task with two repetitions of the target items was used. The interpretation of the results was focused on brain areas that have been previously reported to be involved in explicit memory. Encoding of novel words in comparison with the first repetition was associated with a stronger activation in the left parahippocampal and inferior frontal gyrus. Encoding of novel words compared to the second repetition was related to a greater bifrontal activation. Recognition of studied items was associated with greater activation in the medial and bilateral inferior parietal lobe at first repetition and in the medial and left inferior parietal lobe at second repetition in comparison with encoding of the novel items. Recognition at first repetition compared to recognition at second repetition was associated with greater bilateral frontal activation. The results are discussed in relation to current concepts of spatial differentiation of memory function and findings from event-related potentials studies of continuous recognition.

The effect of immediate and delayed word repetition on event-related potential in a continuous recognition task

The dissociation of immediate and delayed word repetition was studied using a continuous recognition memory task and event-related potential (ERP). Among 240 stimulus words, 40 words were not repeated, 100 were immediately repeated and 100 were repeated after 5 intervening words. Words presented only once during the experiment were referred to as new words. Subjects responded faster and more accurately to words repeated immediately than to new words and to words repeated after a delay. In terms of ERP results, immediate repetition was associated with large P300 amplitude, early P300 latency and the absence of N400, while delayed repetition was associated with small P300 amplitude, late P300 latency and the presence of N400. N400 was elicited only to new words and to those repeated after intervening words. The general morphology of the waveforms was similar for two repetition conditions until around 310 ms after the onset of stimulus. These results indicate that distinct neural systems subserve the immediate and delayed repetition effect, and that the difference between the two emerges around 310 ms poststimulus. Immediate and delayed word repetition are considered in terms of template matching and memory searching, and are possibly mediated by the parietal and left medial temporal lobes, respectively.