Alp Aslan

Prestimulus oscillations predict visual perception performance between and within subjects

In the present study, the electrophysiological correlates of perceiving shortly presented visual stimuli are examined. In particular, we investigated the differences in the prestimulus EEG between subjects who were able to discriminate between four shortly presented stimuli (Perceivers) and subjects who were not (Non-Perceivers). Additionally, we investigated the differences between the subjects perceived and unperceived trials. The results show that Perceivers exhibited lower prestimulus alpha power than Non-Perceivers. Analysis of the prestimulus EEG between perceived and unperceived trials revealed that the perception of a stimulus is related to low phase coupling in the alpha frequency range (8-12 Hz) and high phase coupling in the beta and gamma frequency range (20-45 Hz). Single trial analyses showed that perception performance can be predicted by phase coupling in the alpha, beta and gamma frequency range. The findings indicate that synchronous oscillations in the alpha frequency band inhibit the perception of shortly presented stimuli whereas synchrony in higher frequency ranges (>20 Hz) enhances visual perception. We conclude that alpha, beta and gamma oscillations indicate the attentional state of a subject and thus are able to predict perception performance on a single trial basis.

Part-list cuing as instructed retrieval inhibition

The reexposure of a subset of learned material as a retrieval cue can impair recall of the remaining material. Like part-list relearning—the reexposure of learned material for additional learning—this part-list cuing is often assumed to be the result of output order biases at test, caused by the increased strength of the reexposed material. We directly compared the effects of cuing and relearning when controlling for output order biases. In addition, we compared the two forms of reexposure with the effect of part-list retrieval. Both part-list cuing and part-list retrieval reduced recall performance for the remaining material. By contrast, part-list relearning had no such detrimental effect. These results indicate that the effect of reexposure depends on whether material is reexposed as a cue or for relearning, suggesting that part-list cuing reflects an instructional effect. Evidence is provided that part-list cuing leads to instructed covert retrieval of cue items and causes retrieval inhibition of noncue items, similar to how overt retrieval inhibits nonretrieved items.

Theta oscillations predict the detrimental effects of memory retrieval

Retrieving a target item from episodic memory typically enhances later memory for the retrieved item but causes forgetting of competing irrelevant memories. This finding is termed retrieval-induced forgetting (RIF) and is assumed to be the consequence of an inhibitory mechanism resolving retrieval competition. In the present study, we examined brain oscillatory processes related to RIF, as induced by competitive memory retrieval. Contrasting a competitive with a noncompetitive retrieval condition, we found a stronger increase in early evoked theta (4–7 Hz) activity, which specifically predicted RIF, but not retrieval-induced enhancement. Within the cognitive framework of RIF, these findings suggest that theta oscillations reflect arising interference and its resolution during competitive retrieval in episodic memory. Supplemental materials for this article may be downloaded from http://cabn.psychonomic-journals.org/content/supplemental.

Retrieval-induced forgetting in young children

A prominent theory of cognitive development attributes the poor performance that children show in many cognitive tasks to a general lack of inhibitory control. We tested this theory by examining children’s inhibitory capabilities in retrieval-induced forgetting (RIF), a memory task in which selective retrieval of previously studied material causes forgetting of related, nonretrieved material. Such forgetting is often attributed to inhibitory control processes, which supposedly suppress the nonretrieved items’ memory representation. We examined RIF in kindergartners, second graders, and adults, using both recall and recognition testing. Although all three age groups showed significant RIF in recall, only adults and second graders, but not kindergartners, showed RIF in recognition. Because inhibition-based RIF should be present in recall and recognition, these findings indicate that in adults and second graders, but not in kindergartners, RIF is mediated by inhibition. The results support the view of inefficient inhibitory processes in young children’s cognition.

Part-list cuing can be transient and lasting : The role of encoding

The presentation of a subset of learned items as retrieval cues can have detrimental effects on recall of the remaining items. For 2 types of encoding conditions, the authors examined in 3 experiments whether such part-list cuing is a transient or a lasting phenomenon. Across the experiments, the detrimental effect of part-list cues was consistently found to be transient with a high degree of interim associations and lasting with a low degree. These results indicate that the persistence of part-list cuing depends on encoding, thus challenging both strategy disruption and retrieval inhibition as general accounts of part-list cuing. A 2-mechanism account is provided according to which the 2 mechanisms mediate the effect in different encoding conditions.

The role of inhibitory processes in part-list cuing

Providing a subset of studied items as retrieval cues can have detrimental effects on recall of the remaining items. In 2 experiments, the authors examined such part-list cuing impairment in a repeated testing situation. Participants studied exemplars from several semantic categories and were given 2 successive cued-recall tests separated by a distractor task of several minutes. Part-list cues were provided in the 1st test but not the 2nd. Noncue item recall was tested with the studied category cues (same probes) in the 1st test, but novel, unstudied retrieval cues (independent probes) in the 2nd test. The authors found detrimental effects of part-list cues in both the 1st (same-probe) test and the 2nd (independent-probe) test. These results show that part-list cuing impairment can be lasting and is not eliminated with independent probes. The findings support the view that the impairment was caused by retrieval inhibition.

Memorial consequences of imagination in children and adults

Recent work with adults suggests that imagination can impair later recall of previously encoded events but can improve recall of subsequently encoded events. The present study examined the memorial consequences of imagination in children. Kindergartners, first and fourth graders, and young adults studied two successively presented lists of items. Between the two lists, participants were given an imagination task supposed to create a change in mental context. As expected, in adults, the imagination task impaired recall of the previously encoded material (List 1) and improved recall of the subsequently encoded material (List 2). In children, significant List 1 impairment was present from first grade on, but even fourth graders failed to show improvement for List 2. The results challenge a purely context-based explanation of the memorial costs and benefits of imagination. Instead, they suggest that the two effects are mediated by different mechanisms with different developmental trajectories.

Part-list cuing with and without item-specific probes: the role of encoding

Part-list cuing—the detrimental effect of the presentation of a subset of studied items on recall of the remaining noncue items—was examined in three different study conditions and in the presence and absence of the noncues’ initial letters serving as item-specific probes. With a single study trial, part-list cuing was observed both with and without item-specific probes. By contrast, when participants received two study-test cycles or interrelated list items to a common story, part-list cues were found to be detrimental only in the absence of item-specific probes, but not in their presence. These results indicate that the role of item-specific probes in part-list cuing depends on encoding. The findings are consistent with a recent two-mechanism account of part-list cuing (Bäuml & Aslan, 2006), according to which two different mechanisms mediate the effect in different encoding situations.

Memorial consequences of environmental context change in children and adults

Changing environmental context during encoding can influence episodic memory. This study examined the memorial consequences of environmental context change in children. Kindergartners, first and fourth graders, and young adults studied two lists of items, either in the same room (no context change) or in two different rooms (context change), and subsequently were tested on the two lists in the room in which the second list was encoded. As expected, in adults, the context change impaired recall of the first list and improved recall of the second. Whereas fourth graders showed the same pattern of results as adults, in both kindergartners and first graders no memorial effects of the context change arose. The results indicate that the two effects of environmental context change develop contemporaneously over middle childhood and reach maturity at the end of the elementary school days. The findings are discussed in light of both retrieval-based and encoding-based accounts of context-dependent memory.

Later Maturation of the Beneficial Than the Detrimental Effect of Selective Memory Retrieval

In adults, selective memory retrieval can both impair and improve recall of other memories. The study reported here examined whether children also show these two faces of memory retrieval. Employing a variant of the directed-forgetting task, we asked second, fourth, and seventh graders to study a list of target and nontarget words. After study, the participants received a cue to either forget or continue remembering the list. We subsequently asked some participants to recall the nontarget words before we tested their memory for the target words; for the remaining participants, we tested memory only for the target words. Prior retrieval of nontarget words impaired retrieval of to-be-remembered target words, regardless of children’s age. In contrast, prior retrieval of nontarget words improved recall of to-be-forgotten target words in seventh graders, though not in fourth and second graders. These results suggest a developmental dissociation between the two faces of memory retrieval and indicate later maturation of the beneficial effect than of the detrimental effect of selective memory retrieval.