The effect of retention interval upon hemispheric processes in recognition memory

Is Pupil Activity Associated With the Strength of Memory Signal for Words in a Continuous Recognition Memory Paradigm?

Research on pupillometry provides an increasing evidence for associations between pupil activity and memory processing. The most consistent finding is related to an increase in pupil size for old items compared with novel items, suggesting that pupil activity is associated with the strength of memory signal. However, the time course of these changes is not completely known, specifically, when items are presented in a running recognition task maximizing interference by requiring the recognition of the most recent items from a sequence of old/new items. The sample comprised 42 healthy participants who performed a visual word recognition task under varying conditions of retention interval. Recognition responses were evaluated using behavioral variables for discrimination accuracy, reaction time, and confidence in recognition decisions. Pupil activity was recorded continuously during the entire experiment. The results suggest a decrease in recognition performance with increasing study-test retention interval. Pupil size decreased across retention intervals, while pupil old/new effects were found only for words recognized at the shortest retention interval. Pupillary responses consisted of a pronounced early pupil constriction at retrieval under longer study-test lags corresponding to weaker memory signals. However, the pupil size was also sensitive to the subjective feeling of familiarity as shown by pupil dilation to false alarms (new items judged as old). These results suggest that the pupil size is related not only to the strength of memory signal but also to subjective familiarity decisions in a continuous recognition memory paradigm.

One is all you need: intrahemispheric processing benefits nonverbal visual recognition

Several attempts have been made to understand when and how the two hemispheres of the brain work together to encode and retrieve information during memory tasks, but it remains unclear whether they are equally capable of encoding and retrieval, particularly when the stimuli do not evoke a leftward processing asymmetry. Using a divided visual field paradigm, we presented nonverbal visual stimuli to one visual field/hemisphere at encoding, and at retrieval presented the stimuli either to the same or opposite visual field/hemisphere. Recognition responses were faster and more accurate when the stimuli were initially presented at encoding and retrieval to the same hemisphere (Experiment 1), even when delay intervals between study and test were short (Experiment 2). Taken together, these findings suggest that recognition decisions for stimuli initially presented to a single hemisphere occur more quickly at shorter lags, perhaps due to a stronger memory representation in the original hemisphere of input compared to the indirectly activated hemisphere. Our results are significant because they demonstrate that each hemisphere of the brain can function to encode and retrieve memory representations equally well, as long as the stimuli contain no linguistic information.

Hemispheric asymmetry in recognition memory: effects of retention level on the recognition of Portuguese words

Early findings from Broca and Wernicke led to the classical view of hemispheric specialization, where the main idea relates to left-hemisphere language capabilities compared to right-hemisphere visual capabilities. Federmeier and Benjamin (2005) have suggested that semantic encoding for verbal information in the right hemisphere can be more effective when memory demands are higher. In light of this, our main goal was to study the effect of retention level of verbal information on hemispheric processes. However, regarding the cross-linguistic differences in orthography and their subsequent effects on word recognition (Frost, Katz, & Bentin, 1987), our intent was also to test prior predictions of Federmeier and Benjamin (2005) for a "shallow" orthography language, where words have a clear correspondence between graphemes and phonemes, as opposed to English, which is a "deep" orthography language. Portuguese concrete nouns were selected. The participants were submitted to a visual half-field word presentation using a continuous recognition memory paradigm. The retention level included 1, 2, 4, 8, 20 or 40 words. Results showed that recognition accuracy was higher for words studied in the right visual field, compared to those studied in the left visual field, when the retention interval included 2, 4, or 20 words. No significant differences were found for the remaining intervals. Further analysis on accuracy data for intermediate retention levels showed that recognition accuracy was higher for the 2 words retention level than for the levels including 4, 8, or 20 words; it was higher for left-hemisphere encoding as well. Our results also indicated that reaction times were slower for left-hemisphere encoding and for the 40 words retention level when compared to that of 20 words. In summary, the current results are in partial agreement with those of Federmeier and Benjamin (2005) and suggest different hemispheric memory strategies for the semantic encoding of verbal information.

Do our brain hemispheres exchange some stimulus aspects better than others?

The communication between the two brain hemispheres involves considerable information losses. This study investigated whether these losses might be reduced for frequently processed stimulus attributes and currently attended stimulus properties. It was assumed that size should be more often processed than animateness, since estimating object size is essential for motor planning. Thus, if the transfer deficits were curbed for frequently processed stimulus aspects, then they should be smaller for size than for animateness. By contrast, if the transfer losses were reduced for currently attended stimulus features, then they should depend on the task: in a size judgement task they should be smaller for size, and in an animateness judgement task they should be smaller for animateness. To test the interhemispheric transmission of the two stimulus properties, a lateralized priming paradigm was implemented, in which one group of participants judged targets according to their size and another group according to their animateness. It was found that the transfer deficits were virtually absent for size, but very pronounced for animateness. Hence, the present data provide the first evidence that interhemispheric transmission losses vary for particular stimulus features and that they may be reduced with practice. Since there was no priming for unattended stimulus properties, it remains open whether attention to certain stimulus aspects can improve the interhemispheric exchange as well.

Left and right memory revisited: electrophysiological investigations of hemispheric asymmetries at retrieval

Hemispheric differences in the use of memory retrieval cues were examined in a continuous recognition design, using visual half-field presentation to bias the processing of test words. A speeded recognition task revealed general accuracy and response time advantages for items whose test presentation was biased to the left hemisphere. A second experiment recorded event-related brain potentials in the same design and replicated these behavioral effects, but found no electrophysiological support for the hypothesis that test words biased to the left hemisphere elicit superior recognition. Instead, successful retrieval was accompanied by memory components of identical strength regardless of test field. That robust visual field effects in response accuracy and speed were not mimicked in memory components that generally do correlate with such behavioral differences suggests that patterns in overt responses may be dominated by the left hemisphere's superior ability to apprehend words. Differences between the data pattern observed in the present study with lateralized retrieval and that in a prior study with lateralized encoding [Evans, K. M., & Federmeier, K. D. (2007). The memory that's right and the memory that's left: Event-related potentials reveal hemispheric asymmetries in the encoding and retention of verbal information. Neuropsychologia 45(8), 1777-1790.] support the notion that hemispheric processing is highly integrated in the intact brain, and highlight the need to treat lateralization at different stages as distinct.

Thinking ahead: the role and roots of prediction in language comprehension

Reviewed are studies using event-related potentials to examine when and how sentence context information is used during language comprehension. Results suggest that, when it can, the brain uses context to predict features of likely upcoming items. However, although prediction seems important for comprehension, it also appears susceptible to age-related deterioration and can be associated with processing costs. The brain may address this trade-off by employing multiple processing strategies, distributed across the two cerebral hemispheres. In particular, left hemisphere language processing seems to be oriented toward prediction and the use of top-down cues, whereas right hemisphere comprehension is more bottom-up, biased toward the veridical maintenance of information. Such asymmetries may arise, in turn, because language comprehension mechanisms are integrated with language production mechanisms only in the left hemisphere (the PARLO framework).

The memory that's right and the memory that's left: event-related potentials reveal hemispheric asymmetries in the encoding and retention of verbal information

We examined the nature and timecourse of hemispheric asymmetries in verbal memory by recording event-related potentials (ERPs) in a continuous recognition task. Participants made overt recognition judgments to test words presented in central vision that were either novel (new words) or had been previously presented in the left or right visual field (old words). An ERP memory effect linked to explicit retrieval revealed no asymmetries for words repeated at short and medium retention intervals, but at longer repetition lags (20-50 intervening words) this 'old/new effect' was more pronounced for words whose study presentation had been biased to the right hemisphere (RH). Additionally, a repetition effect linked to more implicit recognition processes (P2 amplitude changes) was observed at all lags for words preferentially encoded by the RH but was not observed for left hemisphere (LH)-encoded words. These results are consistent with theories that the RH encodes verbal stimuli more veridically whereas the LH encodes in a more abstract manner. The current findings provide a critical link between prior work on memory asymmetries, which has emphasized general LH advantages for verbal material, and on language comprehension, which has pointed to an important role for the RH in language processes that require the retention and integration of verbal information over long time spans.

The time course of hemispheric differences in categorical and coordinate spatial processing

Spatial relations between objects can be represented either categorically or coordinately. The metric, coordinate representation is associated with predominant right hemisphere activity, while the abstract, qualitative categorical representation is thought to be processed more in the left hemisphere [Kosslyn, S. M. (1987). Seeing and imagining in the cerebral hemispheres: A computational analysis. Psychological Review, 94, 148-175]. This hypothesized lateralization effect has been found in a number of studies, along with indications that specific task demands can be crucial for these outcomes. In the current experiment a new visual half field task was used which explores these hemispheric differences and their time course by means of a match-to-sample design. Within retention intervals that were brief (500 ms), intermediate (2000 ms), or long (5000 ms), the processing of categorical and coordinate representations was studied. In the 500 ms interval, the hemispheric effect suggested by Kosslyn (1987) was found, but in the longer intervals it was absent. This pattern of the lateralization effect is proposed to be caused by the differential effect the retention interval has on coordinate and categorical representations. Coordinate spatial relations appear susceptible to changes in retention interval and decay very quickly over time, congruent with previous findings about accurate location memory. The processing of categorical spatial relations showed less decay and only between 2000 ms and 5000 ms. Qualitative self reports suggest that the decay found for categorical relations might be caused by a switch from a visual to a more verbal memorization strategy.

Hemispheric asymmetries in the time course of recognition memory

Hemispheric specialization has been studied extensively within subfields ranging from perception to language comprehension. However, the study of asymmetries for basic memory functions--an area that holds promise for bridging these low- and high-level cognitive domains--has been sporadic at best. We examined each hemisphere's tendency to retain verbal information over time, using a continuous recognition memory task with lateralized study items and central test probes. We found that the ubiquitous advantage of the left hemisphere for the processing and retention of verbal information is attenuated and perhaps even reversed over long retention intervals. This result is consistent with theories that propose differences in the degree to which the hemispheres maintain veridical versus semantically transformed representations of the input they receive.

Both sides get the point: Hemispheric sensitivities to sentential constraint

Behavioral studies have consistently reported striking differences in the impact of sentence-level information on the processing of words presented in the right (RVF) versus the left (LVF) visual field, with context effects apparent only for RVF items. The consistent lack of such effects in the LVF has been taken to mean that right hemisphere language comprehension is largely insensitive to message-level meaning. We used the functional specificity afforded by event-related potential measures to assess this claim. Target words completing strongly and weakly constraining sentence contexts, in which constraint arose at the sentence level rather than from lexical associations, were presented laterally in the LVF or RVF. Increased constraint significantly reduced N400 amplitudes with presentation in both VFs, with no differences in the timing or amplitude of these effects. These results are inconsistent with the view that the VF asymmetries found in behavioral measures reflect differential hemispheric capacities at the level of semantic analysis and integration, although VF-based differences on earlier components (P2) suggest asymmetries in the impact of sentential context on perceptual aspects of word processing in the two hemispheres.

Detour behaviour, imprinting and visual lateralization in the domestic chick

Detour behaviour was studied in chicks faced with a vertical-bar barrier behind where an imprinting object (a red ball) was located. Right-eyed chicks took less time to detour the barrier than left-eyed chicks, and binocular chicks showed a bias to detour the barrier on the left side, thus maintaining visual contact with the imprinting object using the lateral field of the right eye, while circling around the barrier. In males, the asymmetries were consistent all along the first two weeks of life, whereas in females they disappeared on days 8 and 11. When tested with a slightly novel version of the original imprinting object (i.e., a ball of a different color), binocular chicks showed a bias to detour the barrier on the right side, thus showing preferential use of the left eye. The same bias occurred when unfamiliar conspecifics were used as goal-objects. Results suggest that cerebral lateralization in birds can directly affect visually-guided motor responses through selective use of the lateral field of vision of the eye contralateral to the hemisphere which has to be put in charge of control of overt behaviour.

Left and Right Hemisphere Memory Traces: Their Formation and Fate. Evidence From Events During Memory Formation in the Chick

In the domestic chick, different versions of a particular learning experience are elaborated by right and left hemispheres (left: selection of cues allowing selection of appropriate response; right: elaboration of relatively complete and unselected record). During memory formation, further processing of the traces is associated with a series of brief points of trace reactivation, which recur with differing periodicity in association with the two hemispheres (16 min: left; 25 min: right). As a result there is a series of near coincidences, which allow interaction between the two traces. The first, at 48-50 min, is associated with such marked changes in what is available to recall that it has been identified as the onset of long-term memory. The period is shown here to begin with a left hemisphere event, which overlaps with a right hemisphere event, beginning at 50 min, in a way that helps to explain why the interaction that occurs at this time is predominantly one in which the left hemisphere accesses right hemisphere material. It is argued that the main change during hemispheric interaction is the establishment of linkages between different trace ''fragments''.

Visual memory lateralization in pigeons

Previous experiments employing simple visual discrimination tasks have revealed a cerebral lateralization in the visual system of pigeons with a dominance of the left hemisphere. Until now, visual memory lateralization in birds has not been investigated. To study possible asymmetries of visual memory functions, a simultaneous instrumental discrimination procedure was used. The animals were trained to discriminate 100 different visual patterns from a further 625 similar stimuli. Retention tests were conducted under binocular and monocular conditions. When the subjects looked monocularly, retention performance was significantly higher with the right eye (left hemisphere) than with the left eye (right hemisphere). The results suggest that the lateralization of the pigeon's visual system depends at least partly on an asymmetry in visual memory capacity.

A Basic Program for the Construction of Controlled-Lag Item-Repetition Sequences

A controlled-lag procedure is a particularly powerful and efficient means of investigating the effects of item repetition as a function of time or material intervening between the repetitions. For example, subjects may be presented with a continuous sequence of items and required to indicate whether each item is new (first presentation) or old (second presentation). The lag between the first and second presentations can be manipulated as a variable in the design. The major disadvantage of this approach is the difficulty of constructing appropriate sequences. A BASIC program is described which automatically constructs sequences of any length given experimental design specifications entered by the user.

Hemispheric asymmetry in tactile forgetting induced by tactually-guided movement

Asymmetries in tactile short-term memory related to differential specialization of the cerebral hemispheres were studied in normal human adults using the Brown-Peterson distractor task. When the distractor was an auditory arithmetic task, no difference emerged between the two hands for the retention of touches to the fingers; however, when the distractor was a tactual maze task executed by the right hand, asymmetry in favor of the left hand was observed. Specifically, when the right hand performed the tactual maze, there was greater interference with tactile memory than when the left hand performed the maze, independent of which hand received the memory material. The results support a characterization of short-term memory as embracing multiple, limited storage capacities divided along the lines of processing demands, arising from different classes of material, placed on the two cerebral hemispheres.

Memory systems in the chick: dissociations and neuronal analysis

Young domestic chicks learn to recognize the visual characteristics of an object to which they are exposed. A restricted part of the forebrain, the intermediate and medial part of the hyperstriatum ventrale (IMHV) is implicated in this process. This form of exposure learning can be dissociated from (i) the ability to learn certain procedures or skills, and (ii) a predisposition to attend to particular types of naturalistic objects. The first of these dissociations is reminiscent of that found in certain human organic amnesias, whilst the second may have its counterpart in the processes involved in face recognition by infants. The right and left IMHV play different roles in the memory that underlies imprinting. The cellular and molecular processes involved in this form of memory are discussed.