Regine Bader

Recognition memory for one-trial-unitized word pairs: Evidence from event-related potentials

Performance in tests of associative memory is generally thought to require recollection while familiarity cannot support memory for associations. However, recent research suggested that familiarity contributes to associative memory when the to-be-associated stimuli are unitized during encoding. Here, we investigated the electrophysiological correlates of retrieval of word pairs after two different encoding conditions. Semantically unrelated word pairs were presented as separate lexical units in a sentence frame (non-unitized word pairs) or together with a definition that allows to combine word pairs to a new concept (unitized word pairs). At test, participants discriminated between word pairs that appeared in the same pairing during study, recombined, or new pairs. Memory processes were examined by means of event-related potentials (ERPs). An early old/new effect with a parietal maximum was found for unitized word pairs while a qualitatively different late old/new effect was elicited by non-unitized word pairs, only. These findings suggest that one-trial-unitized word pairs are recognized differently from non-unitized word pairs. We will discuss the possibility that unitization leads to the engagement of specific forms of familiarity-conceptual fluency and absolute familiarity.

The FN400 is functionally distinct from the N400

The FN400 refers to the early midfrontally-distributed difference between ERPs elicited by old and new items, which operates in a way consistent with a neural marker of familiarity-based recognition. Double dissociations between the FN400 and a later ERP index of recollection provide some of the most compelling evidence in support of dual-process models to date. It has recently been claimed, however, that there is no evidence that the FN400 is functionally distinct from the N400 index of implicit semantic priming (Voss, J., and Federmeier, K., FN400 potentials are functionally identical to N400 potentials and reflect semantic processing during recognition testing, Psychophysiology, 48, 532-546, 2011), challenging inferences made on the basis of this effect. We argue that the design employed to make this claim is flawed because it comprised a semantic priming manipulation embedded within a continuous recognition test which enabled recognition contrasts to be confounded by semantic processes in a number of ways. Here, ERPs were recorded from a design which avoided these confounds by employing a semantic priming paradigm which also served as the encoding phase for a surprise subsequent recognition test phase. An N400 effect elicited in the semantic priming task demonstrated the established centro-parietal maximum, whereas the difference between correctly responded to old and new ERPs in the recognition test was maximal over frontal sites in the same time window. When direct comparisons of the electrophysiological correlates of semantic priming and episodic recognition are recorded in a paradigm in which the two are not confounded, the FN400 reflects a qualitatively distinct effect from the N400.

Selection in touch : Negative priming with tactile stimuli

Abundant experimental evidence has demonstrated attentional selection within the visual modality. Furthermore, the consensus view is currently that two processes contribute to selection: the amplification of the target stimuli and the ignoring (or suppression) of any distractor information. However, at present it is less clear how selection is achieved within the tactile modality. In the present study, we analyze the aftereffects of ignoring tactile distractors, in a novel tactile variant of the negative priming paradigm. In the typical negative priming paradigm, repeating an ignored distractor stimulus as the target on the following trial usually leads to a cost in terms of reaction times (RTs) or error rates, thereby indicating that selection is achieved in part by the ignoring of distractors. In two experiments, we observed significant RT costs when a previously ignored vibrotactile stimulus constituted the target in the next trial. This result shows that tactile selection is in part achieved by active ignoring of distractor representations, as has been shown previously in both the visual and auditory modalities.

Multiple ways to the prior occurrence of an event: An electrophysiological dissociation of experimental and conceptually driven familiarity in recognition memory

Recent research has shown that familiarity contributes to associative memory when the to-be-associated stimuli are unitized during encoding. However, the specific processes underlying familiarity-based recognition of unitized representations are still indefinite. In this study, we present electrophysiologically dissociable early old/new effects, presumably related to two different kinds of familiarity inherent in associative recognition tasks. In a study-test associative recognition memory paradigm, we employed encoding conditions that established unitized representations of two pre-experimentally unrelated words, e.g. vegetable-bible. We compared event-related potentials (ERP) during the retrieval of these unitized word pairs using different retrieval cues. Word pairs presented in the same order as during unitization at encoding elicited a parietally distributed early old/new effect which we interpret as reflecting conceptually driven familiarity for newly formed concepts. Conversely, word pairs presented in reversed order only elicited a topographically dissociable early effect, i.e. the mid-frontal old/new effect, the putative correlate of experimental familiarity. The late parietal old/new effect, the putative ERP correlate of recollection, was obtained irrespective of word order, though it was larger for words presented in same order. These results indicate that familiarity may not be a unitary process and that different task demands can promote the assessment of conceptually driven familiarity for novel unitized concepts or experimentally-induced increments of experimental familiarity, respectively.

More ways than one: ERPs reveal multiple familiarity signals in the word frequency mirror effect

Recent dual-process models of the word frequency mirror effect place absolute familiarity, an item׳s baseline familiarity at a given time point, as responsible for false alarm differences and recollection for hit rate differences between high and low frequency items. One of the earliest dual-process propositions, however, posits an additional relative familiarity mechanism which is sensitive to recent presentation but relative to the absolute familiarity of a particular item (Mandler, 1980). In this study, it was possible to map these three mechanisms onto known event-related potential (ERP) effects in an old/new recognition task with high and low frequency words. Contrasts between ERPs elicited by high and low frequency new items were assumed to index absolute familiarity, and the distribution of this effect from 300 to 600ms was topographically distinct from a temporally-overlapping midfrontally-distributed old/new effect which was larger for low than high frequency words, as would be expected from a relative familiarity mechanism. A later left parietal old/new effect, strongly linked to recollection, was only present for low frequency items. These frequency-sensitive amplitude differences for both old/new effects disappeared in a second recognition task in which old/new decisions were made under a time constraint, although the posterior absolute familiarity effect remained unaffected by the speeding of responses. The data support the assertion that three distinct recognition processes are affected by word frequency in recognition memory tasks, and the qualitatively distinct distributions associated with the two familiarity contrasts support the presence of two cognitively distinct familiarity mechanisms.

Is a novel conceptual unit more than the sum of its parts?: FMRI evidence from an associative recognition memory study.

Recollection, an effortful process relying on the integrity of a brain network including the hippocampus, is generally required to remember arbitrary associations whereas a simple familiarity signal arising in the perirhinal cortex is sufficient to recognize single items. However, the integration of separate items into a single configuration (unitization) leads to reduced involvement of recollection and greater reliance on familiarity. This seems to imply that unitized associations are processed similar to single items. Here, using functional magnetic resonance imaging, we investigated the effects of unitization as encoding strategy on retrieval processes in a between-group-design. A definition was provided that allows combining two unrelated words into a novel conceptual unit (e.g., milk taxi = a delivery service, which is directly dispatched from a farm). We compared this to an encoding strategy in which the words were studied as parts of a sentence. We included pairs in reversed order at test because reversing a unitized word pair is assumed to disrupt the unit while leaving item familiarity for the single constituents intact. This enabled us to compare recognition memory for novel units and single items. Sentence encoding led to a flexible recruitment of brain areas previously associated with recollection, irrespective of the order of the test pair. Unitization encoding reduced the involvement of the recollection network and specifically engaged regions within the parahippocampal cortex and the medial prefrontal cortex for novel units. In contrast, recognition of reversed pairs involved activation of BA 45 in the left inferior frontal gyrus. This possibly suggests that familiarity for novel units and single items are associated with different brain networks.

Separating Event-related Potential Effects for Conceptual Fluency and Episodic Familiarity

ERP old/new effects have been associated with different subprocesses of episodic recognition memory. The notion that recollection is reflected in the left parietal old/new effect seems to be uncontested. However, an association between episodic familiarity and the mid-frontal old/new effect is not uncontroversial. It has been argued that the mid-frontal old/new effect is functionally equivalent to the N400 and hence merely reflects differences in conceptual fluency between old and new items. Therefore, it is related to episodic familiarity only in situations in which conceptual fluency covaries with familiarity. Alternatively, the old/new effect in this time window reflects an interaction of episodic familiarity and conceptual processing with each making a unique functional contribution. To test this latter account, we manipulated conceptual fluency and episodic familiarity orthogonally in an incidental recognition test: Visually presented old and new words were preceded by either conceptually related or unrelated auditory prime words. If the mid-frontal old/new effect is functionally distinguishable from conceptual priming effects, an ERP contrast reflecting pure priming (correct rejections in the related vs. unrelated condition) and a contrast reflecting priming plus familiarity (hits in the related vs. correct rejections in the unrelated condition) should differ in scalp distribution. As predicted, the pure priming contrast had a right-parietal distribution, as typically observed for the N400 effect, whereas the priming plus familiarity contrast was significantly more frontally accentuated. These findings implicate that old/new effects in this time window are driven by unique functional contributions of episodic familiarity and conceptual processing.

The Effect of Unitizing Word Pairs on Recollection Versus Familiarity-Based Retrieval - Further Evidence From ERPs

We investigated the contribution of familiarity and recollection to associative retrieval of word pairs depending on the extent to which the pairs have been unitized through task instructions in the encoding phase. Participants in the unitization condition encoded word pairs in the context of a definition that tied them together such that they were treated as a coherent new item, while in the control condition word pairs were inserted into a sentence frame in which each word remained an individual unit. Contrasting event-related potentials (ERERPs) elicited in a subsequent recognition test by old (intact) and recombined (a new combination of two words from different study pairs) word pairs, an early frontal effect, the putative ER P correlate of familiarity-based retrieval, was apparent in the unitization condition. The left parietal old/new effect, reflecting recollection-based retrieval, was elicited only in the control condition. This suggests that in the unitization condition only, familiarity was sufficiently diagnostic to distinguish old from recombined pairs, while in the control condition, recollection contributed to associative recognition. Our findings add to a body of literature suggesting that unitization of associations increases the relative contribution of familiarity to subsequent associative retrieval.

Age effects on associative memory for novel picture pairings

Normal aging is usually accompanied by greater memory decline for associations than for single items. Though associative memory is generally supported by recollection, it has been suggested that familiarity can also contribute to associative memory when stimuli can be unitized and encoded as a single entity. Given that familiarity remains intact during healthy aging, this may be one route to reducing age-related associative deficits. The current study investigated age-related differences in associative memory under conditions that were expected to differentially promote unitization, in this case by manipulating the spatial arrangement of two semantically unrelated objects positioned relative to each other in either spatially implausible or plausible orientations. Event-related potential (ERP) correlates of item and associative memory were recorded whilst younger and older adults were required to discriminate between old, recombined and new pairs of objects. These ERP correlates of item and associative memory did not vary with plausibility, whereas behavioral measures revealed that both associative and item memory were greater for spatially plausible than implausible pair arrangements. Contrary to predictions, older adults were less able to take advantage of this memory benefit than younger participants. Potential reasons for this are considered, and these are informed by those lines of evidence which indicate older participants were less sensitive to the bottom-up spatial manipulation employed here. It is recommended that future strategies for redressing age-related associative deficits should take account of the aging brains increasing reliance on pre-existing semantic associations.

ERP Subsequent Memory Effects Differ between Inter-Item and Unitization Encoding Tasks

The “subsequent memory paradigm” is an analysis tool to identify brain activity elicited during episodic encoding that is associated with successful subsequent retrieval. Two commonly observed event-related potential “subsequent memory effects” (SMEs) are the parietal SME in the P300 time window and the frontal slow wave SME, but to date a clear characterization of the circumstances under which each SME is observed is missing. To test the hypothesis that the parietal SME occurs when aspects of an experience are unitized into a single item representation, while inter-item associative encoding is reflected in the frontal slow wave effect, participants were assigned to one of two conditions that emphasized one of the encoding types under otherwise matched study phases of a recognition memory experiment. Word pairs were presented either in the context of a definition that allowed to combine the word pairs into a new concept (unitization or item encoding) or together with a sentence frame (inter-item encoding). Performance on the recognition test did not differ between the groups. The parietal SME was only found in the definition group, supporting the idea that this SME occurs when the components of an association are integrated in a unitized item representation. An early prefrontal negativity also exhibited an SME only in this group, suggesting that the formation of novel units occurs through interactions of multiple brain areas. The frontal slow wave SME was pronounced in both groups and may thus reflect processes generally involved in encoding of associations. Our results provide evidence for a partial dissociation of the eliciting conditions of the two types of SMEs and therefore provide a tool for future studies to characterize the different types of episodic encoding.