Beta Oscillations Distinguish Between Two Forms of Mental Imagery While Gamma and Theta Activity Reflects Auditory Attention

Visual sensory processing of external events decreases when attention is internally oriented toward self-generated thoughts and also differences in attenuation have been shown depending on the thought’s modality (visual or auditory thought). The present study aims to assess whether such modulations occurs also in auditory modality. In order to investigate auditory sensory modulations, we compared a passive listening condition with two conditions in which attention was internally oriented as a part of a task; a visual imagery condition and an inner speech condition. EEG signal was recorded from 20 participants while they were exposed to auditory probes during these three conditions. ERP results showed no differences in N1 auditory response comparing the three conditions reflecting maintenance of evoked electrophysiological reactivity for auditory modality. Nonetheless, time-frequency analyses showed that gamma and theta power in frontal regions was higher for passive listening than for internal attentional conditions. Specifically, the reduced amplitude in early gamma and theta band during both inward attention conditions may reflect reduced conscious attention of the current auditory stimulation. Finally, different pattern of beta band activity was observed only during visual imagery which can reflect cross-modal integration between visual and auditory modalities and it can distinguish this form of mental imagery from the inner speech. Taken together, these results showed that attentional suppression mechanisms in auditory modality are different from visual modality during mental imagery processes. Our results about oscillatory activity also confirm the important role of gamma oscillations in auditory processing and the differential neural dynamics underlying the visual and auditory/verbal imagery

Differential Impact of Interference on Internally- and Externally-Directed Attention.

Attention can be oriented externally to the environment or internally to the mind, and can be derailed by interference from irrelevant information originating from either external or internal sources. However, few studies have explored the nature and underlying mechanisms of the interaction between different attentional orientations and different sources of interference. We investigated how externally- and internally-directed attention was impacted by external distraction, how this modulated internal distraction, and whether these interactions were affected by healthy aging. Healthy younger and older adults performed both an externally-oriented visual detection task and an internally-oriented mental rotation task, performed with and without auditory sound delivered through headphones. We found that the addition of auditory sound induced a significant decrease in task performance in both younger and older adults on the visual discrimination task, and this was accompanied by a shift in the type of distractions reported (from internal to external). On the internally-oriented task, auditory sound only affected performance in older adults. These results suggest that the impact of external distractions differentially impacts performance on tasks with internal, as opposed to external, attentional orientations. Further, internal distractibility is affected by the presence of external sound and increased suppression of internal distraction

The assessment of verbal and imaginal encoding processes in the bizarreness effect

The bizarreness effect refers to the finding that sentences that are contrary to the expectations or general world knowledge (e.g. The dog rode the bicycle down the street) produce superior memory as compared to mundane and schema-consistent sentences (e.g. The dog chased the bicycle down the street). There are two major accounts that try to explain the role of the encoding processes in the emergence of the bizarreness effect. The imaginal encoding accounts contend that increased visual processing for the bizarre sentences is responsible for the superior memory. The verbal rehearsal accounts, on the other hand, argue for the role of increased verbal elaboration processes for the bizarre items in the emergence of the bizarreness effect. This project aimed to discourage one of the processes during sentence encoding through the use of a concurrent working memory (WM) task known to selectively impair either verbal or visual WM, to investigate whether the size of the bizarreness effect decreases in any of the distraction conditions. Using tasks such as visual dynamic noise (Experiment 1), spatial tapping (Experiment 2) and visual patterns task (Experiment 3 & 6) that are well known to disrupt visual processing selectively, there was no decrement in the size of the bizarreness effect. Similarly, using tasks such as irrelevant speech (Experiment 1), articulatory suppression (Experiment 2) and letter span task (Experiment 4 & 7) that are well known to disrupt verbal processing selectively, there was no decrement in the size of the bizarreness effect. The results strongly argue against the role of visual and verbal WM processes in the emergence of the bizarreness effect. The results are discussed in terms of Baddeley's working memory model and the attentional accounts of the bizarreness effect

Attentional Demands of Movement Observation as Tested by a Dual Task Approach

Movement observation (MO) has been shown to activate the motor cortex of the observer as indicated by an increase of corticomotor excitability for muscles involved in the observed actions. Moreover, behavioral work has strongly suggested that this process occurs in a near-automatic manner. Here we further tested this proposal by applying transcranial magnetic stimulation (TMS) when subjects observed how an actor lifted objects of different weights as a single or a dual task. The secondary task was either an auditory discrimination task (experiment 1) or a visual discrimination task (experiment 2). In experiment 1, we found that corticomotor excitability reflected the force requirements indicated in the observed movies (i.e. higher responses when the actor had to apply higher forces). Interestingly, this effect was found irrespective of whether MO was performed as a single or a dual task. By contrast, no such systematic modulations of corticomotor excitability were observed in experiment 2 when visual distracters were present. We conclude that interference effects might arise when MO is performed while competing visual stimuli are present. However, when a secondary task is situated in a different modality, neural responses are in line with the notion that the observers motor system responds in a near-automatic manner. This suggests that MO is a task with very low cognitive demands which might be a valuable supplement for rehabilitation training, particularly, in the acute phase after the incident or in patients suffering from attention deficits. However, it is important to keep in mind that visual distracters might interfere with the neural response in M1

Visuo-spatial working memory

This study set out to investigate the visuo-spatial component of Baddeley and Hitch's (1974) Working Memory framework. The development of our understanding of this component has been less dramatic than that of its verbal counterpart, the Articulatory Loop. The primary reason for this can be said to be the lack of techniques for investigation (Logie, 1986). This thesis presents one attempt to try to explore the nature of this code and to reveal possible new techniques of investigation. The following are three possible areas of investigation : 1. Is the system spatially or visually based? 2. Does movement have a role in the system? 3. How is information stored? The latter two issues are investigated here. Experiments 1-4 set out to explore the possibility that movement may be involved in the code. These experiments supported the idea that movement has a role to play in spatial coding and more specifically demonstrated that arm movements which are not compatible with the presentation of spatial material can cause disruption. In addition it was shown that when movement identical to that involved in presentation is encouraged at recall subjects show marked improvement in performance. Together these results very strongly suggest that movement should be given prominent reference in the definition of spatial coding and in the description of the visuo-spatial slave system. Another development that came out of these experiments relates to the lack of investigative techniques in the field of visuo-spatial short term memory. The fact that movement has been shown to be important suggests that techniques employed to investigate kinaesthetic memory will aid us in exploring visuo-spatial coding. The second issue in this thesis explored further the nature of the internal code. Research into the nature of coding in visuo-spatial memory had previously argued for the presence of a sequential component. Experiments 1-4 in this thesis had shown that movement had an important role to play in coding. The fact that movement by its very nature would appear to be sequential suggested that there was a strong sequential element in coding within visuo-spatial memory. However, concern was expressed that the materials and presentation format used may have led to sequential coding. This was first explored in experiments 5-8. The results supported the view that the material and presentation format used had led to sequential coding. This was further explored by Experiments 9 and 10 which illustrated that while it may be important under certain conditions, sequentiality is not always a dominant element in coding within the Visuo-Spatial Sketch Pad. This thesis has explored two of the central issues currently interesting theorists of Working Memory and has put forward suggestions for techniques which may in the future help us to advance our knowledge of the visuo-spatial component of the Working Memory framework

Exploring a Process-Based Account of the Disruption to Music Cognition by Task-Irrelevant Sound

This thesis aimed to explore the extent to which background melody and lyrics—alone or combined within song—impact differentially on concurrent cognitive processes. Current theoretical accounts question specificity for music and language by arguing that lexical, phonological, and music processing share a common cerebral network: yet other lines of evidence indicate that separate working memory processes for music and visual-verbal information exist. However, most prior research addressing interference produced by music on task performance has focused on short-term memory recall/recognition of visually presented tones/words. Few studies address vocal production of melody/lyrics and consequently it is still unclear how pathways for vocal input/output are generated and how the vocal-motor planning mechanism required for vocal production is affected by the competing motor-plan from the presence of extraneous sound. These studies are the first to demonstrate effects of to-be-ignored distracters on long-term memory retrieval and production of songs through humming and speaking performance. Results suggest an independence of language and melody processing and are consistent with an interference-by-process framework. However, further short-term memory tasks provide some evidence against the interference-by-process view. The results extend the perceptual-gestural view of short-term memory, according to which the disruption observed by task-irrelevant sound reflects a clash between the action of the sequencing processes embodied within perceptual input-processing and gestural output-planning systems that are general and co-opted to meet task demands

Working memory constellations

Evidence is presented that supports the view that most models of short-term memory cannot account for the flexibility of the primary memory system. It is argued that the working memory model outlined by Baddeley and Hitch (1974) is, however, a potentially adequate model. Working memory, in this thesis, is depicted as a system that assembles 'constellations' consisting of the central executive and one or more sub-systems. This view suggests a formulation that is considerably more complex than the 1974 model. The empirical studies examine the role of the visuo-spatial scratch pad in the formation and maintenance of working memory constellations. It is concluded from these studies that the scratch pad is independent of the articulatory loop but is usually coupled to the central executive except during maintenance rehearsal. Furthermore, it can be used concurrently with the articulatory loop to process spatial aspects of highly verbal tasks. However a constellation consisting of the executive, the loop and the scratch pad is vulnerable to a wider range of interference effects than a simpler constellation. Paivio (1971) suggested that 'dual coding' leads to better memory performance, however, this is only the case when no distractors are present. The final two chapters present some speculations on how working memory research might proceed in the future. It is concluded that the current trend towards collecting convergent evidence and the emphasis on testing theory in applied situations should give us insights into memory that were not available to Ebbinghaus and other early memory researchers