Helen Gaeta, David Friedman, & Gregory Hunt Cognitive Electrophysiology Laboratory

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

2. Introduction

3. 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 P32 or Psw).

4. 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. • P32 amplitude is sometimes enhanced when the eliciting stimulus is presented for a second time. • The enhanced P32 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 P32 amplitude is enhancedwhen environmental sounds also serveas targets.

5. Method

6. Participants: 24 young adults (mean age = 22.2 years). Stimuli: 50 unique pure tones range 300 - 2750 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 Stimulus category Stimulus prob. Stimulus type Condition 1 (N =12) Condition 2 (N =12) Standard .8 1000 or 700 Hz tone 1000 or 700 Hz tone Target .1 48 environmental sounds (32 presented twice) 48 pure tones (32 presented twice) Novel .1 48 pure tones (32 presented twice) 48 environmental sounds (32 presented twice)

7. 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 1st and 2nd presentations of target and novel stimuli.

8. Results

9. Figure 1.Grand average waveforms for the two experimental conditions. Experiment 1 Environmental target Tone series novel Experiment 2 Tone series target Environmental novel AM2 Novelty P3 AM3 Cz P32 PM15 PM14 0 400 800 ms 0 400 800 ms Novels Targets + 10 mV -

10. 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. 20 Posterior Mean Novelty P3 amplitude (mVs) 15 10 Anterior 5 Tone series Environmental sounds 0 EX.1 EX.2 Targets Novels

11. Table 1. Mean percentage hits, percentage false alarms (FAs), and reaction times (RTs) for the two experimental conditions. Measure Condition 1 (N = 12) Condition2 (N = 12) Mean Mean All stimulus presentations Reaction time (ms) 555.3 498.2 % Hits 96.1 97.9 % False Alarms 6.3 9.1 1st presentation (rare stimuli only) Reaction time (ms) 565.3 491.6 % Hits 95.3 97.1 % False Alarms 9.9 18.1 2nd presentation (rare stimuli only) Reaction time (ms) 546.9 507.9 % Hits 97.1 98.2 % False Alarms 2.6 0.3

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

13. Figure 3. Grand average waveforms superimposed for 1st and 2nd presentations of target and novel stimuli. Environmental Sounds Tone Series Targets RT2 RT2 PM15 RT1 RT1 P32 Novels PM15 + 10 µV - 0 400 800 ms 0 400 800 ms 2nd presentation 1st presentation

14. Statistical Results (ERP and behavior) Reaction times • RTs for environmental targets decreased from 1st to 2nd presentation. • RTs for tone series targets increased from 1st to 2nd presentation. P32 amplitude • Targets > novels regardless of stimulus type. • Environmental sounds > tone series stimuli. • No real difference between 1st and 2ndnovel presentations for either stimulus types. • 2nd presentation for targets > 1st presentations. P32 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.

15. Figure 4. Current source density (CSD) maps for Novelty P3 (260- 360 ms) and P32 for targets and novelselicited by each stimulus type. (scale = 0.05mV/cm2) Novelty P3 P32 Environmental Tone series Environmental 500-600 Tone series 500-600 Targets Anterior aspect of Novelty P3 Posterior P32 Novels Tone series Environmental Tone series 455-555 Environmental 500-600

16. 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 P32 mirror those for Novelty P3.

17. Discussion

18. 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. P32 amplitude was enhanced by repetition of environmental targets but not novels. Thus, the results are equivocal with respect to P32 as an index of semantic processing However, peak latencies for P32s elicited by targets correlated with RTs. This suggests that P32 may reflect a process associated with the guidance and monitoring of the target response.

19. 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, 462-475. Friedman, D., Cycowicz, Y., & Gaeta, H. (in press). The Novelty P3. An event-related potential (ERP) sign of the brain’s evaluation to novelty. Neuroscience and Biobehavioral Reviews.