Edmund Wascher

Improvement and impairment of visually guided behavior through LTP- and LTD-like exposure-based visual learning.

Cellular studies have focused on long-term potentiation (LTP) and long-term depression (LTD) to understand requirements for persistent changes in synaptic connections. Whereas LTP is induced through high-frequency intermittent stimulation, low-frequency stimulation evokes LTD. Because of the ubiquitous efficacy of these protocols, they are considered fundamental mechanisms underlying learning. Here we adapted LTP/LTD-like protocols to visual stimulation to alter human visually guided behavior. In a change-detection task, participants reported luminance changes against distracting orientation changes. Subsequently, they were exposed to passive visual high- or low-frequency stimulation of either the relevant luminance or irrelevant orientation feature. LTP-like high-frequency protocols using luminance improved ability to detect luminance changes, whereas low-frequency LTD-like stimulation impaired performance. In contrast, LTP-like exposure of the irrelevant orientation feature impaired performance, whereas LTD-like orientation stimulation improved it. LTP-like effects were present for 10 days, whereas LTD-like effects lasted for a shorter period of time. Our data demonstrate that instead of electrically stimulating synapses, selective behavioral changes are evoked in humans by using equivalently timed visual stimulation, suggesting that both LTD- and LTP-like protocols control human behavior but that the direction of changes is determined by the feature incorporated into the stimulation protocol.

Age related strategic differences in processing irrelevant information.

Deficient control of irrelevant information with greater age can be demonstrated in paradigms like inhibition of return (IOR). IOR is a mechanism to protect the organism from redirecting attention to a previously scanned irrelevant location and is assumed to be generated slower but to a comparable amount with increasing age. We investigated this putative deficit by means of event-related potentials (ERPs). As expected, IOR developed later in older subjects. In the cue-related ERPs, young subjects showed a large frontocentral N2 (reflecting control or inhibition) which was virtually absent in the old subjects. Instead, the older subjects showed a P3b, reflecting controlled processing of information. Thus, older adults process irrelevant stimuli more like relevant ones, thereby overloading their information processing system.

Differential Effects of Motor Efference Copies and Proprioceptive Information on Response Evaluation Processes

It is well-kown that sensory information influences the way we execute motor responses. However, less is known about if and how sensory and motor information are integrated in the subsequent process of response evaluation. We used a modified Simon Task to investigate how these streams of information are integrated in response evaluation processes, applying an in-depth neurophysiological analysis of event-related potentials (ERPs), time-frequency decomposition and sLORETA. The results show that response evaluation processes are differentially modulated by afferent proprioceptive information and efference copies. While the influence of proprioceptive information is mediated via oscillations in different frequency bands, efference copy based information about the motor execution is specifically mediated via oscillations in the theta frequency band. Stages of visual perception and attention were not modulated by the interaction of proprioception and motor efference copies. Brain areas modulated by the interactive effects of proprioceptive and efference copy based information included the middle frontal gyrus and the supplementary motor area (SMA), suggesting that these areas integrate sensory information for the purpose of response evaluation. The results show how motor response evaluation processes are modulated by information about both the execution and the location of a response.

On the fate of non-cued mental representations in visuo-spatial working memory: Evidence by a retro-cuing paradigm.

By means of a visual retro-cuing paradigm, we investigated the influence of working memory representations that are not required for an ongoing task. A retro-cue reliably indicated the items on the left or right side of a memory array that remained relevant for a subsequent recognition task. On ERP level, the attentional selection of cued memory contents was reflected by a contralateral negativity that appeared at temporal sites in an interval following retro-cue presentation (i.e., 200-400ms). Additionally, the retro-cue caused a suppression of posterior induced alpha power contralateral to the relevant memory items reflecting the release of non-cued information from active maintenance in visuo-spatial working memory. Following the retro-cue, a central probe item was presented and participants had to state whether this stimulus was previously shown on the relevant side of the memory array. The probe was either a cued memory item (cued probe), non-cued memory item (non-cued probe) or was not shown in the previous memory array (new probe). While the same response was required, the non-cued probe condition featured slower response times referred to the new probe condition. In line with these results, a comparison of the probe-locked ERPs pointed toward additional memory retrieval and conflict control mechanisms when processing non-cued probes compared to new probes. Thus although retro-cues were used to drop non-cued information from working memory, it still interfered with the processing of new sensory information based on residual spatial representations in a passive and fragile short-term memory store.

ERP correlates of auditory goal-directed behavior of younger and older adults in a dynamic speech perception task

The ability to understand speech under adverse listening conditions deteriorates with age. In addition to genuine hearing deficits, age-related declines in attentional and inhibitory control are assumed to contribute to these difficulties. Here, the impact of task-irrelevant distractors on speech perception was studied in 28 younger and 24 older participants in a simulated cocktail party scenario. In a two-alternative forced-choice word discrimination task, the participants responded to a rapid succession of short speech stimuli (on and off) that was presented at a frequent standard location or at a rare deviant location in silence or with a concurrent distractor speaker. Behavioral responses and event-related potentials (mismatch negativity MMN, P3a, and reorienting negativity RON) were analyzed to study the interplay of distraction, orientation, and refocusing in the presence of changes in target location. While shifts in target location decreased performance of both age groups, this effect was more pronounced in the older group. Especially in the distractor condition, the electrophysiological measures indicated a delayed attention capture and a delayed re-focussing of attention toward the task-relevant stimulus feature in the older group, relative to the young group. In sum, the results suggest that a delay in the attention switching mechanism contribute to the age-related difficulties in speech perception in dynamic listening situations with multiple speakers.

On the neural mechanisms underlying the protective function of retroactive cuing against perceptual interference: Evidence by event-related potentials of the EEG

This EEG study investigated the protective effect of retroactive attentional focusing on working memory. To this effect, we used a visuo-spatial working memory task and presented block-wise distractor displays after working memory contents had been updated by means of a retroactive cue (retro-cue). Retroactive attention attenuated the interfering effect of distractors on memory precision. The reduction of working memory load by means of a selective retro-cue was reflected by a decline of a negative slow wave over parietal sites. Posterior N1 to the distractor was reduced following a selective retro-cue compared to a neutral retro-cue condition, most notably at left hemispheric sites. P3b referred to the distractor was suppressed completely only following a selective retro-cue. This suggests that focusing on only a subset of visuo-spatial information represented in working memory releases cognitive resources for preventing the in-depth processing of subsequently irrelevant visual events, thereby inhibiting their transfer into working memory.

From Capture to Inhibition: How does Irrelevant Information Influence Visual Search? Evidence from a Spatial Cuing Paradigm.

Even though information is spatially and temporally irrelevant, it can influence the processing of subsequent information. The present study used a spatial cuing paradigm to investigate the origins of this persisting influence by means of event-related potentials (ERPs) of the EEG. An irrelevant color cue that was either contingent (color search) or non-contingent (shape search) on attentional sets was presented prior to a target array with different stimulus-onset asynchronies (SOA; 200, 400, 800 ms). Behavioral results indicated that color cues captured attention only when they shared target-defining properties. These same-location effects persisted over time but were pronounced when cue and target array were presented in close succession. N2 posterior contralateral (N2pc) showed that the color cue generally drew attention, but was strongest in the contingent condition. A subsequently emerging contralateral posterior positivity referred to the irrelevant cue (i.e., distractor positivity, Pd) was unaffected by the attentional set and therefore interpreted as an inhibitory process required to enable a re-direction of the attentional focus. Contralateral delay activity (CDA) was only observable in the contingent condition, indicating the transfer of spatial information into working memory and thus providing an explanation for the same-location effect for longer SOAs. Inhibition of this irrelevant information was reflected by a second contralateral positivity triggered through target presentation. The results suggest that distracting information is actively maintained when it resembles a sought-after object. However, two independent attentional processes are at work to compensate for attentional distraction: the timely inhibition of attentional capture and the active inhibition of mental representation of irrelevant information.

Compliance instead of flexibility? On age-related differences in cognitive control during visual search

The effect of healthy aging on cognitive control of irrelevant visual information was investigated by using event-related potentials. Participants performed a spatial cuing task where an irrelevant color cue that was either contingent (color search) or noncontingent (shape search) on the attentional set was presented before a target with different stimulus-onset asynchronies. In the contingent condition, attentional capture appeared independent of age and persisted over the stimulus-onset asynchronies but was markedly pronounced for elderly people. Accordingly, event-related potential analyses revealed that both older and younger adults initially selected the irrelevant cue when it was contingent on the attentional set and transferred spatial cue information into working memory. However, only younger adults revealed inhibitory mechanisms to compensate for attentional capture. It is proposed that this age-related lack of reactive inhibition leads to stickiness in visual processing whenever information is contingent on the attentional set, unveiling older adults Achilles heel in cognitive control.

On the contribution of motor planning to the retroactive cuing benefit in working memory: Evidence by mu and beta oscillatory activity in the EEG

&NA; Attention can be allocated toward mental representations in working memory also after the initial encoding of information has been completed. It was shown that focusing on only one item within working memory transfers this representation into a protected state, reducing its susceptibility to interference by incoming signals. The present study investigated the nature of this retroactive cue (retro‐cue) benefit by means of oscillatory activity in the EEG. In a working memory task with a retro‐cue indicating one, two or three memory representations as relevant and a block‐wise distractor display presented after the retro‐cue, participants had to remember the orientation of a colored bar. On behavioral level, we found that the interfering effect of the distractor display on memory performance could be prevented when a retro‐cue reduced the number of attended representations in working memory. However, only the one‐item retro‐cue led to an overall increase in task performance compared to a condition without a retro‐cue. The neural basis of this special representational status was investigated by means of oscillatory parameters in the EEG and a clustering approach on level of the independent components (ICs) in the signal. The retroactive reduction of attended working memory representations was reflected in a suppression of alpha power over right parietal and parieto‐occipital sites. In addition, we found that an IC cluster representing oscillatory activity in the mu/beta range (10–12 Hz and 20–24 Hz) with a source in sensorimotor cortex revealed a power suppression already prior to the memory probe following the one‐item retro‐cue. This suggests that the retro‐cue benefit results in large parts from the possibility to focus attention on one particular item in working memory and initiate motor planning processes already ahead of the probe stimulus indicating the respective response. HighlightsThe retro‐cue benefit is related to a head start of response planning.This mechanism can be used when the desired response is obvious after a retro‐cue.Contralateral mu/beta suppression reflects the response planning head start.The source of mu/beta suppression is located in sensorimotor cortex.

Psychologie und Gehirn 2007

Thus, audio-visual motion integration influences the perceptual stage of motion processing. In contrast, conflicting motion increases fronto-parietal activation which possibly reflects decisional processes. In sum, we interpret the observed activation shift from auditory to visual motion areas during CMDC as reflecting a competition between senses for the final motion percept that is possibly regulated by attention.