Perceptual processing in dichotic listening.

Subjects heard two lists of 4 items each presented simultaneously to the two ears at a rate of four pairs of items per sec. A recall cue presented immediately after the test list signalled report of 4 of the 8 items. In recall by spatial location, the cue indicated whether the items on the right ear on left ear should be recalled. In recall by category name, the cue indicated the superset category (e.g., letters or words) of the items to be recalled. Recall by spatial location was not significantly different than recall by category name. This results argues against the idea of a preperceptual auditory storage that holds information along spatial channels for 1 or 2 sec. The final experiment showed that recall by spatial location is significantly better than recall by category name when the report cue is given before, not after, the list presentation. These results show that spatial location can be used to enhance semantic processing and/or memory of 1 of 2 simultaneous items, but only if the relevant location is known at the time of the item presentation.     

Hemispheric asymmetries in auditory distraction

Serial-verbal short-term memory is impaired by irrelevant sound, particularly when the sound changes acoustically (the changing-state effect). In contrast, short-term recall of semantic information is impaired only by the semanticity of irrelevant speech, particularly when it is semantically related to the target memory items (the between-sequence semantic similarity effect). Previous research indicates that the changing-state effect is larger when the sound is presented to the left ear in comparison to the right ear, the left ear disadvantage. In this paper, we report a novel finding whereby the between-sequence semantic similarity effect is larger when the irrelevant speech is presented to the right ear in comparison to the left ear, but this right ear disadvantage is found only when meaning is the basis of recall (Experiments 1 and 3), not when order is the basis of recall (Experiment 2). Our results complement previous research on hemispheric asymmetry effects in cross-modal auditory distraction by demonstrating a role for the left hemisphere in semantic auditory distraction.     

Time in the eye of the beholder: Gaze position reveals spatial-temporal associations during encoding and memory retrieval of future and past

Time is grounded in various ways, and previous studies point to a “mental time line” with past associated with the left, and future with the right side. In this study, we investigated whether spontaneous eye movements on a blank screen would follow a mental timeline during encoding, free recall, and recognition of past and future items. In all three stages of processing, gaze position was more rightward during future items compared to past items. Moreover, horizontal gaze position during encoding predicted horizontal gaze position during free recall and recognition. We conclude that mental time line and the stored gaze position during encoding assist memory retrieval of past versus future items. Our findings highlight the spatial nature of temporal representations.     

Levels of processing with free and cued recall and unilateral temporal lobe epilepsy

This study investigates the role of the temporal lobes in levels-of-processing tasks (phonetic and semantic encoding) according to the nature of recall tasks (free and cued recall). These tasks were administered to 48 patients with unilateral temporal epilepsy (right "RTLE"=24; left "LTLE"=24) and a normal group (n=24). The results indicated that LTLE patients were impaired for semantic processing (free and cued recall) and for phonetic processing (free and cued recall), while for RTLE patients deficits appeared in free recall with semantic processing. It is suggested that the left temporal lobe is involved in all aspects of verbal memory, and that the right temporal lobe is specialized in semantic processing. Moreover, our data seem to indicate that RTLE patients present a retrieval processing impairment (semantic condition), whereas the LTLE group is characterized by encoding difficulties in the phonetic and semantic condition.     

Information processing and speech lateralization in learning-disabled children

The relationship between information processing and speech lateralization was investigated in learning-disabled children. The Kaufman Assessment Battery for Children (K-ABC) assessed simultaneous and successive processing while a dichotic listening paradigm with free recall and directed attention conditions assessed speech lateralization. A three-factor ANOVA design conducted on the dichotic data revealed that normal children demonstrated stronger right ear advantage (REA); whereas learning-disabled showed weaker right ear advantage. Further, lambda analyses conducted on individual subjects revealed that the learning-disabled did not demonstrate the REA, were not biased attenders, and did not get more right ear than left ear items when attention was directed to one ear. Multiple-regression analysis was used to predict sequential processing from the dichotic data for both groups. Learning-disabled children demonstrated a substantial deficit in sequential processing as compared to normal children. These results indicate that learning-disabled children may not have adequate cerebral lateralization of receptive speech processes, shift their attention more readily, and are more inadequate in sequential processing that presumably subserves language functioning. Perhaps learning-disabled children have deficiencies of processor capacity of salient areas of the left (language) hemisphere.     

Lateralized impairment of the emotional enhancement of verbal memory in patients with amygdala-hippocampus lesion

This study investigated amygdala-hippocampus's functional asymmetry in the emotional modulation of memory for stories. Thirty-nine, right-handed, drug-resistant epilepsy patients who had been submitted to unilateral temporal lobectomy (19 left and 20 right) watched either an arousing or neutral version of a story presented audio-visually. The slide sequence was the same in the neutral and arousing version, the narratives were matched for structure and comprehensibility. The set and order of the 11 slide sequence were identical in both conditions. Free recall and recognition measures were taken 2h after story presentation. Subjects in the TLE group who watched the arousing version recalled more details than the subjects who watched the neutral version (t(37)=3.4,p<.001). The group who watched the arousing version recalled more details of the phase 2 of the story (t(37)=6.76,p<.001). Scores in both conditions did not differ between control subjects and temporal lobectomy patients. When the right and left lesioned groups' results were analyzed separately, it was observed that the two groups did not differ in their recall of the neutral version. The right lesioned group recalled more items of the arousal than the neutral version (Z=-3.55,p<.001). However the left lesioned group did not show the memory enhancement for the emotional version, in this group it was only found an enhanced recall of the more pictorial emotional segment of the narrative (Z=-3.11,p<.001). This illustrates that the right amygdala can influence retention of complex emotional stimuli with verbal and pictorial arousing properties. We concluded that an intact left amygdala-hippocampus is important for enhancement of memory related to emotionally arousing verbal material.     

Retention of attended and unattended auditorily and visually presented material

In the first of two experiments investigating focussed attention, sets of four pairs of digits were dichotically presented to subjects who were instructed to attend to digits arriving in either the left or the right ear. Following presentation, two different report orders were used: attended followed by unattended, and unattended followed by attended. It was found that unattended items did not suffer from being recalled second rather than first. The serial position curve for unattended items was U-shaped. These results were interpreted as evidence that unattended items are not retained in a limited-capacity auditory buffer with a fast rate of loss. The experiment was repeated using visually presented pairs of letters. A similar pattern of results was obtained, consistent with the hypothesis that unattended items are recalled from a store with a large capacity and a very slow rate of loss.     

Modality effects in delayed free recall and recognition: Visual is better than auditory

During presentation of auditory and visual lists of words, different groups of subjects generated words that either rhymed with the presented words or that were associates. Immediately after list presentation, subjects recalled either the presented or the generated words. After presentation and test of all lists, a final free recall test and a recognition test were given. Visual presentation generally produced higher recall and recognition than did auditory presentation for both encoding conditions. The results are not consistent with explanations of modality effects in terms of echoic memory or greater temporal distinctiveness of auditory items. The results are more in line with the separate-streams hypothesis, which argues for different kinds of input processing for auditory and visual items.     

Auditory attentional capture during serial recall: violations at encoding of an algorithm-based neural model?

A novel attentional capture effect is reported in which visual-verbal serial recall was disrupted if a single deviation in the interstimulus interval occurred within otherwise regularly presented task-irrelevant spoken items. The degree of disruption was the same whether the temporal deviant was embedded in a sequence made up of a repeating item or a sequence of changing items. Moreover, the effect was evident during the presentation of the to-be-remembered sequence but not during rehearsal just prior to recall, suggesting that the encoding of sequences is particularly susceptible. The results suggest that attentional capture is due to a violation of an algorithm rather than an aggregate-based neural model and further undermine an attentional capture-based account of the classical changing-state irrelevant sound effect.     

Right-ear advantage and delayed recall

Two studies were performed using monaural presentation of verbal material to test for a right-ear advantage (REA) in recall. It was hypothesized that a delayed recall task and examination of the serial position curve would be a more sensitive test for ear asymmetries than those used in previous studies. In Experiment 1, 30 right-handed male subjects were given lists of words to recall, presented to either the left or right ear, with language chatter, baroque music, or no stimulus concurrently presented to the opposite ear. Both immediate and delayed recall were assessed. The results indicated that the strongest REAs appeared in delayed recall. Moreover, the REAs occurred regardless of the stimulus conditions co-occurring in the other ear. Experiment 2 was done to test whether the REAs in the delayed recall were due to rehearsal biases. Twenty-four right-handed male subjects recalled lists of words with standard instructions and instructions to recall in the reverse order of input (limiting rehearsal). The results indicated that the backward instructions limited and controlled rehearsal and, hence, input to long-term storage; the REAs occurred in delayed recall under all instructional conditions.     

Time,space, and memory for order

Information about the order of items in a sequence can be conveyed either spatially or temporally. In the present investigation, we examined whether these different modes of presentation map onto compatible mental representations of serial order. We examined this issue in three immediate serial-recall experiments, in which participants recalled lists of letters in the temporal order in which they had appeared. Each letter in a to-be-remembered sequence was presented in a unique spatial position, with the order of these spatial positions progressing from either left to right or right to left. In this way, the visually presented lists contained both temporal and spatial order information. Recall of the temporal order information was more accurate with congruent spatial order information—that is, when the letters progressed from left to right, following the typical reading direction of English—than when the spatial order information was incongruent. These results suggest compatible representations of serial order when sequences are conveyed spatially and temporally.     

Accuracy of recognition for speech presented to the right and left ears

Earlier reports by other authors had shown that recall of dichotically presented speech was better for words arriving at the right ear, while recognition of passages of music was better for music presented to the left ear. It seemed desirable to test recognition for speech, in order to show that the difference between materials rather than the difference in testing techniques was responsible for this disparity between ears.

Accordingly 18 men were presented with dichotic lists of digits, and then tested for recognition of the digits. There was no indication of an advantage for the left ear, but rather of the advantage for the right already established for recall of speech materials.     

Interference with Rehearsal in Spatial Working Memory in the Absence of Eye Movements

We have previously argued that rehearsal in spatial working memory is interfered with by spatial attention shifts rather than simply by movements to locations in space (Smyth & Scholey, 1994). It is possible, however, that the stimuli intended to induce attention shifts in our experiments also induced eye movements and interfered either with an overt eye movement rehearsal strategy or with a covert one. In the first experiment reported here, subjects fixated while they maintained a sequence of spatial items in memory before recalling them in order. Fixation did not affect recall, but auditory spatial stimuli presented during the interval did decrease performance, and it was further decreased if the stimuli were categorized as coming from the right or the left. A second experiment investigated the effects of auditory spatial stimuli to which no response was ever required and found that these did not interfere with performance, indicating that it is the spatial salience of targets that leads to interference. This interference from spatial input in the absence of any overt movement of the eyes or limbs is interpreted in terms of shifts of spatial attention or spatial monitoring, which Morris (1989) has suggested affects spatial encoding and which our findings suggest also affects reactivation in rehearsal.     

Perceptual identification and encoding

Sequences containing 10 numbers from 1–20 were presented in serial-order or random-order at rates of 1/sec, 2/sec, and 4/sec for serial-order or same-orderrecall by eight Ss. Stimulus duration was constant, so that the interpresentation interval decreased as rate of presentation increased. Serial-order recall was greater for serial-order presentation than for random-order presentation. The decrease in recall as presentation rate increased was similar for both serial-order and random-order presentation. This result indicates that serial-order recall of random-order presentation does not involve reordering or repeated sequential scanning. It is consistent with the view that serial-order recall of serial-order presentation is greater because identification time is decreased. due to the decrease in the range of relevant alternatives, so that increased encoding time results in storage of more information.     

Free recall and retrieval speed of categorized items by kindergarten children

Kindergarten Ss were presented with 16 pictorial items in four category sets or a partially random ordem with one item from each category composing the four presentation sets. The pictures were presented either on conceptually related background pictures or on white backgrounds. The categorically grouped presentation facilitated free recall performance, both in terms of number of items recalled and the speed with which the items were recalled, and increased the amount of clustering in recall. Categorical clustering in recall was associated with shorter within- than between-category intervals and for those Ss who recalled items from each of four categories successively, the over-all temporal pattern in recall closely approximated that found with adults. No background effects were found.     

Backward masking and asymmetry of processing for vowels differing in acoustical similarity

Several investigations have reported problems in demonstrating for vowels the phenomena of backward masking and right ear advantage so easily demonstrated for consonants. An experiment is reported on the dichotic backward masking (BM) of acoustically similar and dissimilar sets of vowels in consonant-vowel syllables. The results suggest that increasing perceptual difficulty by varying the acoustic similarity of the stimulus set augments BM. A second experiment showed that the right ear advantage (REA) was augmented by manipulating the acoustic similarity of the stimulus set and by decreasing intelligibility through the addition of noise. This and other evidence was employed to ascribe variations in both REA and BM to the interaction of perceptual processing time with information decay in precategorical acoustical storage. It is argued that this process interaction underlies statistical interactions in dichotic data which show that variations in difficulty (discriminability, noise addition, brain deterioration) affect most adversely the least favoured items (those presented earlier, those on the unattended ear, those on the left ear).     

Interference within hands: Retrieval-induced forgetting of left and right hand movements

We examined retrieval-induced forgetting of motor sequences that were categorized by the effectors (left or right hand) involved in their execution. This left–right categorization was independent from input locations or input devices. In addition, the acquired motor sequences were arbitrarily assigned to left and right. Participants learned twelve sequential joystick movements as responses to letter stimuli. Half of the sequences pertained to the left, half to the right hand. Subsequent retrieval-practice of half the items of one hand induced forgetting for the non-retrieved rest of the items of that hand in a final recall test. This finding demonstrates that the hands were used to organize the memory storage of motor sequences in a way that gave rise to later interference between commonly stored items, that is, linked to the same hand.     

Electrographic correlates of lateral asymmetry in the processing of verbal and nonverbal auditory stimuli

A veraged evoked potentials (AEP) to verbal (digits) and nonverbal (clicks) auditory stimuli were recorded from left and right temporal leads in ten right-handed Ss. With dichotic presentation, there was no significant difference in accuracy of report of the clicks heard in each ear, but significantly more digits were identified correctly from the right ear than from the left. Dichotic verbal stimuli elicited AEP whose early components were of greater amplitude, and whose later components were of shorter latency, from the left hemisphere than from the right. No consistent latency or amplitude differences were observed between AEP from the left and right hemispheres when clicks were presented dichotically.     

Young children's use of temporal and spatial order information in short-term memory

Encoding and retrieval of temporal and spatial order information was investigated in the free recall and probed recognition performance of 3-, 4-, 5-, and 6-year-olds. In both tasks, three line drawings of familiar objects were presented successively in different spatial locations, so that temporal order was not confounded with spatial order. Subjects of all ages revealed an organization for the stimulus display based on the temporal sequence of presentation. With increasing age, subjects began recall more often with the first item so as to take advantage of this sequential organization. In the probed recognition task, subjects were asked questions requiring the use of temporal or spatial order information. Performance by the older subjects indicated that information about temporal and spatial order could be simultaneously encoded. The results are discussed in terms of a context theory derived from Estes's hierarchical association model.