Helen Gaeta, David Friedman, & Gregory Hunt Cognitive Electrophysiology Laboratory New York State Psychiatric Institute Differential Effects of Stimulus Features and Task Category on the Novelty P3

Introduction

Low-probability task-irrelevant stimuli, that are complex in nature, elicit a positive ERP component (labeled the Novelty P3) when presented embedded within an oddball paradigm. They also elicit a second, longer latency positivity (labeled P3 2 or P sw ).

The Novelty P3 is believed to reflect the neural processes that underpin the cognitive evaluation of unexpected events in the environment. The Novelty P3 is most commonly elicited using complex environmental sounds that convey semantic information. The nature of the eliciting complex environmental sounds makes them sensory- and information- "rich" relative to the invariant, task-relevant pure tone stimuli in which they are embedded. P3 2 amplitude is sometimes enhanced when the eliciting stimulus is presented for a second time. The enhanced P3 2 may be analogous to repetition priming of words evaluated for meaning. Aims To evaluate the contribution of the stimulus nature and task relevance on generation of the Novelty P3. To determine if P3 2 amplitude is enhanced when environmental sounds also serve as targets.

Metho d

Participants:24 young adults (mean age = 22.2 years). Stimuli:50 unique pure tones range Hz in 50 Hz steps duration = 336 ms, 10 ms rise and fall time 48 unique environmental sounds (Fabiani et al., 1996) Task: Button press to designated target stimuli. Paradigm:Novelty Oddball 48 environmental sounds (32 presented twice) 48 pure tones (32 presented twice).1Novel 48 pure tones (32 presented twice) 48 environmental sounds (32 presented twice).1Target 1000 or 700 Hz tone.8Standard Condition 2 (N =12) Condition 1 (N =12) Stimulus typeStimulus prob. Stimulus category

EEG recordings and ERP analysis EEG recordings were obtained from 62 sites referred to nose tip using Ag/AgCl electrodes in an electrocap. Bipolar, horizontal and vertical EOGs were also recorded and used for subsequent artifact correction. (5.3 s time- constant; 30 Hz upper cutoff, sample rate = 200 Hz, 10K amp.). After artifact correction, 1000 ms epochs of ERP data were averaged according to stimulus type. Averages were constructed for each subject from ERPS for standard, target, and novel stimuli. Further averages were constructed for 1 st and 2 nd presentations of target and novel stimuli.

Result s

Figure 1. Grand average waveforms for the two experimental conditions. AM V Cz PM15 PM14 AM ms ms Targets Novels Experiment 1 Environmental target Tone series novel Experiment 2 Tone series target Environmental novel Novelty P3 P3 2

Target s Novels Posterior Anterior Tone series Environmental sounds EX.1EX.2 Mean Novelty P3 amplitude ( Vs ) Figure 2. Plot of Novelty P3 amplitudes. Mean amplitudes are shown for anterior and posterior scalp sites for each type of stimulus and each task category. Statistical results Anterior amplitude of environmental sounds > tone series. Posterior amplitude of targets > novels.

0.32.6% False Alarms % Hits Reaction time (ms)2nd presentation (rare stimuli only) % False Alarms % Hits Reaction time (ms) 1 st presentation (rare stimuli only) % False Alarms % Hits Reaction time (ms)All stimulus presentations Mean Condition 2 (N = 12) Condition 1 (N = 12) Measure Table 1. Mean percentage hits, percentage false alarms (FAs), and reaction times (RTs) for the two experimental conditions.

Statistical Results (behavior) RTs for environmental targets > than for tone series target. RTs decreased from 1 st to 2 nd presentations for environmental targets. RTs increased from 1 st to 2 nd presentations for tone targets. FAs decreased from 1 st to 2 nd presentation for both types of novel stimuli, but the difference was greater for environmental than tones series novels

Figure 3. Grand average waveforms superimposed for 1 st and 2 nd presentations of target and novel stimuli. PM15 Environmental Sounds PM µ V Tone Series ms ms Targets Novels 1 st presentation 2nd presentation P3 2 RT 1 RT 2

Statistical Results (ERP and behavior) Reaction times RTs for environmental targets decreased from 1 st to 2 nd presentation. RTs for tone series targets increased from 1 st to 2 nd presentation. P3 2 amplitude Targets > novels regardless of stimulus type. Environmental sounds > tone series stimuli. No real difference between 1 st and 2 nd novel presentations for either stimulus types. 2 nd presentation for targets > 1 st presentations. P3 2 latencies Peak latencies for environmental sounds > tone series stimuli regardless of task category. Target RTs positively correlate with target ERP peak latencies (Pearson's r =.35, p <.05), but not with novel peak latencies.

Figure 4. Current source density (CSD) maps for Novelty P3 ( ms) and P3 2 for targets and novels elicited by each stimulus type. ( scale = 0.05V/cm 2 ) Novelty P3P3 2 Targets EnvironmentalTone seriesEnvironmental Tone series Novels Tone seriesEnvironmentalTone series Environmental Anterior aspect of Novelty P3Posterior P3 2

CSD analyses Anterior and posterior foci are present in all Novelty P3 CSD maps. The anterior focus is strongest for environmental sounds and weakest for tone series targets. The posterior focus is clearly delineated for all stimuli. Posterior foci for P3 2 mirror those for Novelty P3.

Discussio n

The extent of the anterior aspect of the Novelty P3 was determined mostly by the stimulus nature of the eliciting task, regardless of the task category. The greater the contextual distinctiveness of a low- probability event the greater the extent of the anterior response. The posterior aspect of the Novelty P3 was determined by the task relevance of the stimulus, regardless of the nature of the stimulus. The differential effects of stimulus distinctiveness and task relevance provide evidence that the ERP component that was previously labeled the Novelty P3 is comprised of two components. One component has an anterior focus, whose extent is determined by the contextual distinctiveness of the stimulus, and corresponds to the Novelty P3. The other has a posterior focus, whose extent is determined by the task relevance of the stimulus, and corresponds to the Suttonian P300. Behavioral positive priming was obtained for the environmental targets. P3 2 amplitude was enhanced by repetition of environmental targets but not novels. Thus, the results are equivocal with respect to P3 2 as an index of semantic processing However, peak latencies for P3 2 s elicited by targets correlated with RTs. This suggests that P3 2 may reflect a process associated with the guidance and monitoring of the target response.

CONCLUSION Low-probability deviant stimuli elicit both a Novelty P3 and a P3b ( Friedman et al.,in press ). The extent of each is determined by the contextual salience and the perceived informational relevance of the stimulus. References Fabiani, M., Kazmerski, V., Cycowicz, Y., & Friedman, D. (1996). Naming norms for brief environmental stimuli. Effects of age and dementia. Psychophysiology, 33, Friedman, D., Cycowicz, Y., & Gaeta, H. (in press). The Novelty P3. An event-related potential (ERP) sign of the brains evaluation to novelty. Neuroscience and Biobehavioral Reviews.