Kathrin Lange

Early processing stages are modulated when auditory stimuli are presented at an attended moment in time: an event-related potential study.

The present study investigated with event-related potentials whether attending to a moment in time modulates the processing of auditory stimuli at a similar early, perceptual level as attending to a location in space. The participants listened to short (600 ms) and long (1,200 ms) intervals marked by white noise bursts. The task was to attend in alternating runs either to the short or to the long intervals and to respond to rare offset markers that differed in intensity from the frequent standard offset markers. Prior to the to-be-attended moment, a slow negative potential developed over the frontal scalp. Stimuli presented at the attended compared to the unattended moments in time elicited an enhanced N1 and an enhanced posteriorly distributed positivity (300-370 ms). The results show that attention can be flexibly controlled in time and that not only late but also early perceptual processing stages are modulated by attending to a moment in time.

Early visual deprivation impairs multisensory interactions in humans.

Animal studies have shown that visual deprivation during the first months of life permanently impairs the interactions between sensory systems. Here we report an analogous effect for humans who had been deprived of pattern vision for at least the first five months of their life as a result of congenital binocular cataracts. These patients showed reduced audio-visual interactions in later life, although their visual performance in control tasks was unimpaired. Thus, adequate (multisensory) input during the first months of life seems to be a prerequisite in humans, as well as in animals, for the full development of cross-modal interactions.

Brain correlates of early auditory processing are attenuated by expectations for time and pitch

The present study investigated how auditory processing is modulated by expectations for time and pitch by analyzing reaction times and event-related potentials (ERPs). In two experiments, tone sequences were presented to the participants, who had to discriminate whether the last tone of the sequence contained a short gap or was continuous (Experiment 1: go/nogo, Experiment 2: choice reaction). Expectations were induced by varying the temporal and pitch regularity of the sequence. Results were consistent across both experiments. Expectations for both time and pitch were associated with faster responding. Both temporal and pitch expectations led to an attenuation of the auditory N1, thus indicating a modulation of early, perceptual processing by temporal and pitch expectations. Effects of temporal expectations were also evident in a P300-like deflection, suggesting that temporal expectations also affect decision- or response-related processing stages.

Orienting Attention to Points in Time Improves Stimulus Processing Both within and across Modalities

Spatial attention affects the processing of stimuli of both a task-relevant and a task-irrelevant modality. The present study investigated if similar cross-modal effects exist when attention is oriented to a point in time. Short (600 msec) and long (1200 msec) empty intervals, marked by a tactile onset and an auditory or a tactile offset marker, were presented. In each block, the participants had to attend one interval and one modality. Event-related potentials (ERPs) to auditory and tactile offset markers of attended as compared to unattended intervals were characterized by an enhancement of early negative deflections of the auditory and somatosensory ERPs (audition, 100140 msec; touch, 130180 msec) when audition or touch was task relevant, respectively. Similar effects were found for auditory stimuli when touch was task relevant. An additional reaction time experiment revealed faster responses to both auditory and tactile stimuli at the attended as compared to the unattended point in time, irrespective of which modality was primary. Both behavioral and ERP data show that attention can be focused on a point in time, which results in a more efficient processing of auditory and tactile stimuli. The ERP data further suggest that a relative enhancement at perceptual processing stages contributes to the processing advantage for temporally attended stimuli. The existence of cross-modal effects of temporal attention underlines the importance of time as a feature for binding input across different modalities.

Conceptual priming for environmental sounds and words: an ERP study

In this study we examined conceptual priming using environmental sounds and visually displayed words. Priming for sounds and words was observed in response latency as well as in event-related potentials. Reactions were faster when a related word followed an environmental sound and vice versa. Moreover both stimulus types produced an N400-effect for unrelated compared to related trials. The N400-effect had an earlier onset for environmental sounds than for words. The results support the theoretical notion that conceptual processing may be similar for verbal and non-verbal stimuli.

The ups and downs of temporal orienting: a review of auditory temporal orienting studies and a model associating the heterogeneous findings on the auditory N1 with opposite effects of attention and prediction

The temporal orienting of attention refers to the process of focusing (neural) resources on a particular time point in order to boost the processing of and the responding to sensory events. Temporal attention is manipulated by varying the task-relevance of events at different time points or by inducing expectations that an event occurs at a particular time point. Notably, the electrophysiological correlates of these manipulations at early processing stages are not identical: Auditory studies operationalizing temporal attention through task-relevance consistently found enhancements of early, sensory processing, as shown in the N1 component of the auditory event-related potential (ERP). By contrast, previous work on temporal orienting based on expectations showed mixed results: early, sensory processing was either enhanced or attenuated or not affected at all. In the present work, I will review existing findings on temporal orienting with a special focus on the auditory modality and present a working model to reconcile the previously heterogeneous results. Specifically, I will suggest that when expectations are used to manipulate attention, this will lead both to an orienting of attention and to the generation of precise predictions about the upcoming event. Attention and prediction are assumed to have opposite effects on early auditory processing, with temporal attention increasing and temporal predictions decreasing the associated ERP correlate, the auditory N1. The heterogeneous findings of studies manipulating temporal orienting by inducing expectations may thus be the consequence of differences in the relative contribution of attention and prediction processes. The models predictions will be discussed in the context of a functional interpretation of the auditory N1 as an attention call signal, as presented in a recent model on auditory processing.

The redundant target effect is affected by modality switch costs

When participants have to respond to stimuli of two modalities, faster reaction times are observed for simultaneous, bimodal events than for unimodal events (the redundant target effect [RTE]). This finding has been interpreted as reflecting processing gains for bimodal relative to unimodal stimuli, possibly due to multisensory interactions. In random stimulus sequences, reaction times are slower when the stimulus is preceded by a stimulus of a different modality (modality switch effect [MSE]). Simple reaction time redundant target experiments with auditory-visual, visual-tactile, and auditory-tactile stimulus combinations were run to determine whether the RTE may be partly explained by MSEs because bimodal stimuli do not require a modality switch. In all three modality pairings, significant MSEs and RTEs were observed. However, the RTE was still significant after reaction times were corrected for the MSE, supporting the hypothesis that coactivation occurs independently of modality switch costs.

The reduced N1 to self-generated tones: An effect of temporal predictability?

Tones that are self-generated elicit a smaller N1 than externally triggered tones. Typically, however, self-generated tones are also more predictable in time than externally triggered ones. The present study investigated whether the attenuated N1 can be explained by predictability based on the temporal relationship between action and effect. Participants listened to tones that were self-generated by a key-press or preceded by a visual cue. The tones followed the key-presses or cues after a fixed (predictable context) or variable delay (unpredictable context). Tones triggered by a key-press elicited a smaller N1 than tones following a visual cue. This finding suggests that the reduced N1 to self-generated tones is not merely due to the fact that the tones timing can be predicted based on its temporal relationship to the key-press. Whether a tone was presented in a predictable or an unpredictable context did not affect the N1.

Can a regular context induce temporal orienting to a target sound

It has been shown recently (Lange, 2009) that the N1 of the auditory event related potential (ERP) is attenuated when the eliciting stimulus predictably follows a regular vs. an irregular sequence. This may be a sign of temporal orienting induced by the regular sequence. Alternatively, the attenuated N1 may have been due to sensory predictability of target timing. The present study investigated whether presenting a regular sequence still attenuates target N1 when target timing is unpredictable. A regular (vs. irregular) tone sequence was presented prior to a target tone, which appeared unpredictably at one of three different time points after the sequence. For the regular sequence, targets either continued regularity (on-time targets) or were early or late with respect to this regular time point. ERPs to on-time targets were compared as a function of sequence regularity. Consistent with the assumption that N1 attenuation reflects sensory predictability of target timing, an attenuated N1 was not observed in the present study, where target timing was uncertain.

N400-effects to task-irrelevant environmental sounds: further evidence for obligatory conceptual processing.

We assessed conceptual priming for environmental sounds in two tasks using pairs of a visually presented word (prime) and an environmental sound (probe). In the physical task, participants indicated to which ear the sound was presented. In the semantic task, participants judged whether a word labeled a sound correctly. The physical always preceded the semantic task to exclude semantic carry-over effects. In both tasks prime word color indicated whether a response was required (Go/NoGo-trials). An N400-effect for unrelated vs. related sounds was observed in all four conditions resulting from the combination of both tasks with response requirement. However, the N400-effect was reduced in the physical task and in NoGo-trials. Hence, meaning of environmental sounds may be processed obligatorily. Both automatic and controlled processes mediate the analysis of sound meaning.