Oscillatory activity in prefrontal and posterior regions during implicit letter-location binding.

Many cognitive abilities involve the integration of information from different modalities, a process referred to as "binding." It remains less clear, however, whether the creation of bound representations occurs in an involuntary manner, and whether the links between the constituent features of an object are symmetrical. We used magnetoencephalography to investigate whether oscillatory brain activity related to binding processes would be observed in conditions in which participants maintain one feature only (involuntary binding); and whether this activity varies as a function of the feature attended to by participants (binding asymmetry). Participants performed two probe recognition tasks that were identical in terms of their perceptual characteristics and only differed with respect to the instructions given (to memorize either consonants or locations). MEG data were reconstructed using a current source distribution estimation in the classical frequency bands. We observed implicit verbal-spatial binding only when participants successfully maintained the identity of consonants, which was associated with a selective increase in oscillatory activity over prefrontal regions in all frequency bands during the first half of the retention period and accompanied by increased activity in posterior brain regions. The increase in oscillatory activity in prefrontal areas was only observed during the verbal task, which suggests that this activity might be signaling neural processes specifically involved in cross-code binding. Current results are in agreement with proposals suggesting that the prefrontal cortex function as a "pointer" which indexes the features that belong together within an object.

Odorant Normative Data for Use in Olfactory Memory Experiments: Dimension Selection and Analysis of Individual Differences.

The present study reports normative ratings for 200 food and non-food odors. One hundred participants rated odors across measures of verbalisability, perceived descriptive ability, context availability, pleasantness, irritability, intensity, familiarity, frequency, age of acquisition, and complexity. Analysis of the agreement between raters revealed that four dimensions, those of familiarity, intensity, pleasantness, and irritability, have the strongest utility as normative data. The ratings for the remaining dimensions exhibited reduced discriminability across the odor set and should therefore be used with caution. Indeed, these dimensions showed a larger difference between individuals in the ratings of the odors. Familiarity was shown to be related to pleasantness, and a non-linear relationship between pleasantness and intensity was observed which reflects greater intensity for odors that elicit a strong hedonic response. The suitability of these data for use in future olfactory study is considered, and effective implementation of the data for controlling stimuli is discussed.

The asymmetry and temporal dynamics of incidental letter-location bindings in working memory.

Verbal-spatial bindings are integral to routine cognitive operations (e.g., reading), yet the processes supporting them in working memory are little understood. Campo and colleagues [Campo, P., Poch, C., Parmentier, F. B. R., Moratti, S., Elsley, J. V., Castellanos, N., … Maestú, F. (2010). Oscillatory activity in prefrontal and posterior regions during implicit letter-location binding. Neuroimage, 49, 2807-2815] recently reported data suggesting obligatory letter-location binding when participants were directed to remember the letters in a display (of letters in locations), but no evidence for binding when instructed to remember the filled locations. The present study contrasted two explanations for this binding asymmetry. First, it may result from an obligatory dependence on "where" during the representation of "what" information, while "where" information may be held independently of its contents (the strong asymmetry hypothesis). Second, it may constitute a snapshot of a dynamic feature inhibition process that had partially completed by test: the asymmetrical inhibition hypothesis. Using Campo and colleagues' task with a variable retention interval between display and test, we presented four consonants in distinct locations and contrasted performance between "remember letters" and "remember locations" instructions. Our data supported the strong asymmetry hypothesis through demonstrating binding in the verbal task, but not in the spatial task. Critically, when present, verbal-spatial bindings were remarkably stable, enduring for at least 15 seconds.

Distraction by auditory novelty. The course and aftermath of novelty and semantic effects.

The unexpected occurrence of an oddball auditory stimulus (novel) among an otherwise repeated stream of sounds (standards) is known to impact negatively on participants' performance in an unrelated visual task. The present study sought to test new predictions emerging from Parmentier's (2008) model of distraction by auditory novelty. Participants categorized the direction of visual arrows preceded by a task-irrelevant sound. Two time intervals between distractor and target were tested in separate blocks of trials. Rare auditory novels consisted of the words "left" or "right", which were either congruent or incongruent with the upcoming target. The data confirmed the slowing of response in the face of a novel (novelty distraction) as well as, on incongruent trials, a further delay due to cross-talk interference between distractor and target (semantic effect). More importantly, and in line with our predictions, the results further showed that (1) the semantic effect, but not novelty distraction, increased with the time interval between distractor and target; and that (2) the production of a response on the first standard trial following a novel trial was slowed if that response required the activation of a recently inhibited network (post-novelty semantic effect). Overall, the data lend support to the view that behavioral distraction by auditory novelty reflects a mosaic of contributors, the effects of which can ripple across trials.

A behavioral study of distraction by vibrotactile novelty.

Past research has demonstrated that the occurrence of unexpected task-irrelevant changes in the auditory or visual sensory channels captured attention in an obligatory fashion, hindering behavioral performance in ongoing auditory or visual categorization tasks and generating orientation and re-orientation electrophysiological responses. We report the first experiment extending the behavioral study of cross-modal distraction to tactile novelty. Using a vibrotactile-visual cross-modal oddball task and a bespoke hand-arm vibration device, we found that participants were significantly slower at categorizing the parity of visually presented digits following a rare and unexpected change in vibrotactile stimulation (novelty distraction), and that this effect extended to the subsequent trial (postnovelty distraction). These results are in line with past research on auditory and visual novelty and fit the proposition of common and amodal cognitive mechanisms for the involuntary detection of change.

Why are auditory novels distracting? Contrasting the roles of novelty, violation of expectation and stimulus change.

Past studies show that novel auditory stimuli, presented in the context of an otherwise repeated sound, capture participants' attention away from a focal task, resulting in measurable behavioral distraction. Novel sounds are traditionally defined as rare and unexpected but past studies have not sought to disentangle these concepts directly. Using a cross-modal oddball task, we contrasted these aspects orthogonally by manipulating the base rate and conditional probabilities of sound events. We report for the first time that behavioral distraction does not result from a sound's novelty per se but from the violation of the cognitive system's expectation based on the learning of conditional probabilities and, to some extent, the occurrence of a perceptual change from one sound to another.

Behavioral distraction by auditory novelty is not only about novelty: the role of the distracter's informational value.

Unexpected events often distract us. In the laboratory, novel auditory stimuli have been shown to capture attention away from a focal visual task and yield specific electrophysiological responses as well as a behavioral cost to performance. Distraction is thought to follow ineluctably from the sound's low probability of occurrence or, put more simply, its unexpected occurrence. Our study challenges this view with respect to behavioral distraction and argues that past research failed to identify the informational value of sound as a mediator of novelty distraction. We report an experiment showing that (1) behavioral novelty distraction is only observed when the sound announces the occurrence and timing of an upcoming visual target (as is the case in all past research); (2) that no such distraction is observed for deviant sounds conveying no such information; and that (3) deviant sounds can actually facilitate performance when these, but not the standards, convey information. We conclude that behavioral novelty distraction, as observed in oddball tasks, is observed in the presence of novel sounds but only when the cognitive system can take advantage of the auditory distracters to optimize performance.

Explicit processing of verbal and spatial features during letter-location binding modulates oscillatory activity of a fronto-parietal network.

The present study investigated the binding of verbal and spatial features in immediate memory. In a recent study, we demonstrated incidental and asymmetrical letter-location binding effects when participants attended to letter features (but not when they attended to location features) that were associated with greater oscillatory activity over prefrontal and posterior regions during the retention period. We were interested to investigate whether the patterns of brain activity associated with the incidental binding of letters and locations observed when only the verbal feature is attended differ from those reflecting the binding resulting from the controlled/explicit processing of both verbal and spatial features. To achieve this, neural activity was recorded using magnetoencephalography (MEG) while participants performed two working memory tasks. Both tasks were identical in terms of their perceptual characteristics and only differed with respect to the task instructions. One of the tasks required participants to process both letters and locations. In the other, participants were instructed to memorize only the letters, regardless of their location. Time-frequency representation of MEG data based on the wavelet transform of the signals was calculated on a single trial basis during the maintenance period of both tasks. Critically, despite equivalent behavioural binding effects in both tasks, single and dual feature encoding relied on different neuroanatomical and neural oscillatory correlates. We propose that enhanced activation of an anterior-posterior dorsal network observed in the task requiring the processing of both features reflects the necessity for allocating greater resources to intentionally process verbal and spatial features in this task.

Is verbal-spatial binding in working memory impaired by a concurrent memory load?

Binding processes play a critical role in memory. We investigated whether the binding of (visually presented) verbal and spatial (locations) information involves general attentional resources, as stipulated in the revised working memory model, by comparing measures of binding in the presence and absence of a concurrent memory load. Using an adaptation of a probe recognition task contrasting performance between intact and recombined conditions, we found that the concurrent retention of a sequence of three pure tones eliminated verbal-spatial binding. The present study constitutes the first to directly measure the impact of a concurrent memory load on verbal-spatial binding and suggests that such binding may indeed recruit attentional resources, consistent with some recent findings in the visual-spatial binding literature.