1. Investigating the Negativity Bias Using the Affective Go/No Go and ERPs Jason Krompinger, Jason S. Moser, & Robert F. Simons Department of Psychology, University of Delaware
Abstract
Results
Discussion
Figure 1
Recent studies have used the affective go/no go (AGN) task (i.e., a task involving responding and/or withholding response to affective stimuli) to examine modulations of attention by stimulus valence. Some of these studies show shorter reaction times for positive targets and more commission errors for positive distracters, as evidence for an attentional bias towards positive information among healthy controls. However, past event-related-potential (ERP) studies using similar populations indicate that negative stimuli spontaneously receive more extended processing as indexed by enhanced positive-going attention-related components. This study employed the AGN task and obtained both behavioral and ERP data in order to reconcile such competing hypotheses. Nineteen undergraduates performed the AGN task using arousal-equated positive and negative IAPS pictures while ERPs were collected. Consistent with previous studies, subjects made more commission errors for positive than negative distracters. The P300, however, averaged across all correct trials, was larger for negative than for positive stimuli.  The ERP data suggest that the decreased ability to withhold responses to positive distracters in this active inhibition context is not a result of an attentional bias toward positive stimuli, but rather reflects that negative stimuli command increased perceptual processing resources – thus aiding in task performance. This 'negativity bias' showed the largest effects in a group relatively high on depressive symptomatology.
Results indicate that individuals with mild depressive symptomatology show a bias towards negative as compared to equally arousing positive images.
Conversely, subjects with little to no depressive symptoms exhibited no bias towards either stimulus type.
Perhaps the lack of homogeneity in negativity bias / ERP literature can be explained by subject variability between samples.
-This pattern of results suggests that late ERPs, as compared to behavioral measures, might be sensitive to underlying attentional biases towards emotional information among subjects with mild levels of psychopathology
A more extensive study using a group of depressed and non-depressed subjects is necessary in order to provide further evidence for the utility of ERPs in this regard.
-Results show that early ERP components typically modulated in Go/No Go paradigms (e.g. the N2) are not affected by either trial or valence when using emotional pictures. Perhaps using less complex emotional stimuli will allow for a more fine grained analysis of the effects of emotion on cognitive control mechanisms that are reflected in ERPs.
Subjects ranged from 1-21 on the IDD, were separated into high and low groups via median split (Med = 7, M = 7.57)
Initial ANOVA yielded an overall effect of site (F(3,51)=44, p<.0001), post-hoc t-tests indicated that the P300 was equally large at both Cz and Pz.
We also observed interaction between valence and site (F(3, 51)=4.7, p<.05), indicating that negative pictures elicited larger P300s than positive pictures at site Pz (t(18)=2.1, p<.05).
The initial ANOVA also yielded a Trial X Valence X IDD Group interaction (F(1,16)=5.1, p<.05), indicating that the High IDD group exhibited both a strong trial (t(8)=, p<.05) and valence effect (t(8)=, p<.05) that were not present in the Low IDD group (ts<1).
-Behavioral results yielded no differences in RT between positive and negative targets (t(18)<1)
, Subjects showed more errors of commission for positive than for negative distracters (F(1,17)=7.6, p<.05). No differences existed between IDD groups.
Introduction
- Current data examining the “negativity bias” with affective pictures (IAPS; Lang et al, 1999) and ERPs are inconsistent: some show the effect (e.g. Ito, 1998; Delplanque, 2006; Smith, 2007) while others do not (e.g. Schupp 2000; Cuthbert, 2000).
- One potential confound involves the subjective arousal ratings of the stimuli; it is well-documented that higher-arousing stimuli give rise to larger LPPs regardless of stimulus valence (e.g. Schupp, 2004). Thus, it is critical that positive and negative pictures are equated for arousal.
- Another possibility for the heterogeneous results in previous studies has to do with individual differences among subject populations. Numerous studies show that subjects showing mild to severe levels of depression exhibit attentional biases for negative information (Siegle, 2002, Murphy, 1999), it is possible that these biases are reflected in ERPs elicited by emotional stimuli
- We used a modified affective go/no go task using emotional pictures to observe P300s to positive and negative stimuli in a random sample of undergraduates. We collected information on depressive symptoms in order to determine relationships between these and a bias for negative pictures in the P300.
Methods
-19 students (10 females) in an introductory psychology class participated in the current experiment for course credit
-60 pictures from the International Affective Picture System (IAPS; Lang et al., 1999) were selected—30 pleasant and 30 unpleasant.
-Pictures differed on normative valence ratings (M = 7.01 and 2.22 for pleasant and unpleasant picture content, respectively ), but were rated as equally arousing (M= and , for pleasant and unpleasant picture content, respectively).
-The affective go/no go task consisted of 32 experimental blocks with 20 pictures each. Pictures were presented serially for 300 ms with a 1200 ms ISI. Subjects were to respond, via button press, to the instructed “go” stimuli (either a positive or negative picture) and withold responses to the “no-go” stimuli. 80% of each block were comprised of “go” stimuli and the remaining 20% “no go” stimuli.
-The order of the experimental blocks can be mapped as follows (with P=“go positive” and N= “go negative”): PPNNPPNNPPNN. Thus, each pair consisted of a block requiring a task-switch from the previous block and a block requiring no task-switch.
-All subjects completed the Inventory to Diagnose Depression (IDD; Zimmerman, 1980) following task completion.
-EEG recorded from Fz, FCz, Cz, Pz, A1, and A2 using an ECI electrocap and tin disk electrodes, and bandpass filtered at 20 Hz.
-EEG recorded at 200 samples per second, using VPM software (Cook, 1998); EOG artifacts corrected by method developed by Gratton et al. (1983); Single-trial EEG was lowpass filtered below 20 Hz
-The late P3 was measured at all sites (using a 75 ms pre-stimulus baseline) by computing the average voltage between 480 and 580 ms post-stimulus onset, capturing its peak and subsequent resolution.
-ERPs and behavioral data were statistically evaluated using SPSS (Version 14.0) General Linear Model software with Greenhouse-Geisser corrected p-values
Figure 1A
IDD Median Split
Figure 1B
Figure 1: Overall effects of trial and valence on the P300 at site Pz.
Figure 1a: Trial and valence effects on the P300 at Pz for 10 subjects low on depressive symptoms
Figure 1b: Trial and valence effects on the P300 at Pz for 9 subjects relatively (over 7) high on depressive symptoms.
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