Event-related potentials

The wiki’s first electrocortical method, arriving with Pollatos, Kirsch & Schandry (2005). Its place in this collection is defined by contrast: every other brain measure here (fMRI, PET, lesion, morphometry) trades time for space. ERP trades space for time.

The components that matter in this literature

• N100 (~100-150 ms) — early sensory/perceptual response. In Pollatos et al. interoceptive accuracy had no effect here, which is the paper’s cleanest inference: whatever interoception does to emotional processing, it does late.
• P300 (~290-500 ms) — a large positive deflection, maximal at posterior/parietal sites for visual stimuli. Read as an index of attention, processing capacity, motivational relevance, or task difficulty — the ambiguity is the problem. Larger for emotional than neutral pictures.
• Late positive slow wave (~400 ms onward) — sustained positivity, sensitive to emotional content, interpreted as continued perceptual processing and allocation of resources to motivationally relevant input (Kok 1997; Keil et al. 2002).

Why the N100 null is the most defensible thing ERP contributed here

Worth isolating, because it runs against the usual reading of null results.

Pollatos et al. make several anatomical claims (insula, ACC, medial prefrontal, somatosensory cortices) that their method cannot support — they are imported from Damasio et al. (2000) and PET/fMRI work, and the paper concedes that P300 generator studies disagree with each other before reasoning from them anyway. Those claims are decoration.

The N100 null is not. It requires no source model at all: if interoceptive accuracy modulated the earliest cortical response, an ERP would show it, and it did not. That licenses “interoception enters late” — a claim about timing, which is the one thing this method is authoritative about. On Damasio’s staging that points away from emotion trigger sites and toward first- and second-order structures.

The general lesson for reading this wiki’s ERP content: trust the latency, discount the anatomy.

The between-groups amplitude problem

A caution Pollatos et al. do not raise and which bears on their central ERP finding.

Their P300 effect is a comparison between people — good vs poor heartbeat perceivers — not between conditions within a person. Raw ERP amplitude varies between individuals for reasons with nothing to do with psychology: skull thickness, cortical geometry, electrode impedance, and tonic arousal all scale the recorded voltage. A within-subject condition contrast cancels these; a between-groups contrast does not.

This is exactly why the emotion-specificity of an effect carries the interpretive weight. Their P300 difference appeared across all 60 slides including neutral household objects, which is what a generic amplitude difference between two groups of people looks like. Their slow-wave difference appeared for affective slides and not neutral ones, which is not — a nuisance factor scaling everything cannot produce a condition-selective effect. The slow wave is the finding; the P300 main effect is a group difference of undetermined origin.

Relation to the rest of the wiki’s toolkit

ERP measures the central response to an emotional stimulus. It says nothing about the peripheral response — and Pollatos et al. recorded ECG without ever analysing it against the pictures, so their study has cortex and self-report and no body in between. Compare skin-conductance-response and the cardiac measures in Dunn et al. (2010), which have the body and no cortex. No study in this wiki yet has both.