Sensores de pH

As discussed earlier, valence and arousal are often correlated. For this reason, it is important to consider whether ERPs that are putative markers of emotion — especially, valence- specific effects — are also influenced by arousal, regardless of valence.

Junghöfer, Bradley, Elbert, and Lang (2001) focused on differences in early ERP patterns evoked by stimulus arousal differences. The investigators presented high and low arousal IAPS in rapid succession alternating between arousal levels on trials. Valence differences between the stimuli were not a factor in the investigation and ERP patterns were reported for the posterior region of the scalp. No differences between arousal levels were found during the P100 (96-160 ms) time period. Differences emerged within the P200 (168-232 ms) period and demonstrated low arousal images evoked a more positive component pattern than high arousal images. During the N260 (232-296 ms) period, high arousal images evoked a more negative component than low arousal images. These time periods overlap with the EPN period and possibly represent activation differences of the same processing system. These results suggest the EPN modulation found in ERP patterns is possibly a marker of arousal differences and not valence differences.

Rozenkrantz and Polich (2008) used high and low arousal positive and negative IAPS presented in an oddball detection paradigm. High arousal positive and negative images were matched in arousal level, as were low arousal positive and negative images. They found that the patterns in the EPN window (220-300 ms) evoked by high arousal images were more positive than low arousing images. They also found that the LPP (which encompassed the LPP window: 300-450 ms, the early slow wave: 550-700 ms, and the late slow wave: 700-850 ms) was more positive to high arousing images than low arousing images. Both positive and negative images

held this pattern related to arousal at frontal, central, and posterior sites. these results support a role of arousal in the EPN and LPP.

Hinojosa, Carretié, Valcárcel, Méndez-Bértolo, and Pozo (2009) conducted two experiments. One utilized words, and the other IAPS, in the same methodology. Positive and negative stimuli were matched on arousal (relaxing and neutral were not). For the word experiment, the EPN window (225-275 ms) showed no effects, however for the LPP window (350-425 ms) neutral words evoked more positive patterns than positive and negative words in occipital region and more negativity in frontal region. For the image experiment, the EPN window (175-275 ms) showed that positive images had greater negativity than negative in occipital region, supporting valence specificity in the EPN. The LPP window showed more negative patterns for positive and negative images compared to neutral images in the frontopolar region, and more positive patterns for positive and negative images compared to neutral images in mid-central and mid-parietal regions.

Leite, Carvalho, Galdo-Alvarez, Alves, Sampaio, and Conçalves (2012) used affective pictures that were high and low in arousal during passive viewing and a startle eye-blink task. Compared to neutral, the EPN was sensitive to early attentional allocation directed toward affective stimuli compared to neutral. They also reported an LPP that was larger to high arousing pleasant and unpleasant images compared to low arousal pleasant, unpleasant, and neutral images. The startle probe LPP amplitude was smallest to high arousing pleasant images compared to all other conditions.

Briggs and Martin (2009) selected high and low arousal IAPS that corresponded to positive, negative, neutral, and sexual categories to create eight comparison conditions. The LPP pattern 300-500 ms was evaluated between conditions. High and low neutral images, and high

and low positive images did not differ in LPP amplitude. The LPPs for high arousal sexual and unpleasant images were significantly more positive than low arousal versions. The LPP for high arousal sexual images was significantly more positive than all other conditions. The LPP for high arousal unpleasant images was significantly more positive than for high arousing positive and neutral conditions. Low arousing sexual images evoked more positive patterns than low arousal neutral images. Despite a few exceptions between conditions high arousing stimuli yield larger amplitude patterns. Inferring that sexual and unpleasant stimuli motivate the greatest amount of cognitive resources, followed then by pleasant images, these results are consistent with the LPP indexing the amount of resources garnered for processing effort.

Lithari, Frantzidis, Papadelis, Vivas, Klados, et al. (2010) found the P100 less positive to high arousing images than low arousing images. The N100 showed greater negativity was evoked by high arousing images than low arousing images. The N200 had a shorter latency for high than low arousing images. Furthermore, the LPP evoked by high arousing images was more positive than when evoked by low arousing images.

In general, high arousal stimuli appear to evoke more positive ERP component patterns than lower arousal stimuli. This would be expected as more processing resources should be mobilized and allocated to processing highly arousing stimuli, which are more likely to signal significant events than low arousing stimuli in the environment. The EPN, thought to be an early marker of emotion, is less consistent than the LPP with regard to arousal. The LPP is larger to emotional than neutral stimuli in each of the studies reported, whereas the EPN varied between emotionally arousing and low arousing or neutral categories. These studies indicate that differences found in late ERP patterns attributed to valence differences between positive and negative stimuli must be considered along in light of their arousal differences. Therefore, these

studies underscore the necessity to carefully control affective stimuli on the arousal dimension, or manipulate arousal in conjunction with valence systematically, when investigating affective influences on brain activity to ensure that valid inferences can be drawn about ERP effects. If valence differences are revealed after arousal variation was controlled, the role of emotion in modulating the waveform patterns is more reliably inferred. This methodological imperative applies equally to inferences about behavioral result differences.

Table 1. ERP Effects of Arousal

Paper Stimulus Type Modality Task P1 N1 EPN MFN/N400 LPP

Briggs (2009) pictures visual distractor

(oddball) n.a. n.a n.a. n.a. High A > Low A

Hinojosa (2009) words visual judge

arousal n.a. n.a. n.s. n.a. E > NEUT

Junghöfer (2001) pictures visual passive NS n.a. High A < Med A

<Low A n.a. n.a.

Leite (2012) pictures visual passive n.a. n.a. High A/Low A

< NEU n.a. High A > Low A

Lithari (2010) pictures visual passive High A >

Low A

High A >

Low A n.a.

3

n.a. High A > Low A Rozenkrantz (2008) pictures visual distractor

(oddball) n.a. NS High A > Low A n.a. High A > Low A

Gianotti (2008) words (Exp.1) visual passive NS NS NS NS High A > Low A

pictures (Exp.2) visual passive NS NS Low A > High A NS High A > Low A

1

POS > NEG/NEUT (not a pure effect of arousal)

2

Note. "High A" and "Low A" denote high and low arousal, respectively. In these experiments, arousal was explicitly varied and orthogonal to valence. "E" and "N" denote emotional and neutral. In these experiments, positive and negative stimuli were contrasted with neutral stimuli.

3

Note. Figure 2 shows an arousal effect within the EPN window: the ERP difference topography shows a stronger negativity over parietal region, and a greater positivity over inferior sites. Unfortunately, the direction of the contrast (high A - low A, or low A- high A) is not specified. Therefore, it is not possible to determine whether this effect corresponds with a typical EPN effect.