M2 Process Information and Channel Ablation

In eyeprocess: Harmonize Eye-Tracking, Pupillometry, Biometrics, and Psychometric Process Data

knitr::opts_chunk$set(collapse = TRUE, comment = "#>")

A common response target

The central M2 question is not whether RT and gaze have their own likelihood information. It is whether they improve measurement of the scored-response trait under a joint model.

multimodal_m2_ablation() therefore fits a compatible sequence:

• M0: response only;
• M1: response + RT;
• M2: response + RT + gaze.

multimodal_m2_process_information() compares all three models on the same response observations.

library(eyeprocess)

sim <- simulate_multimodal_m2(
  n_person = 150,
  n_item = 15,
  seed = 220
)

abl <- multimodal_m2_ablation(
  sim,
  chains = 4,
  parallel_chains = 4,
  iter_warmup = 1000,
  iter_sampling = 1000,
  seed = 221
)

info <- multimodal_m2_process_information(abl)
info

plot(info, type = "response_elpd")
plot(info, type = "theta_variance")

Two complementary quantities

The evidence object reports:

1. response-target PSIS-LOO ELPD, using only the scored-response log-likelihood in every model and MCMC relative-efficiency adjustment, for held-out response cells among the observed persons and items;
2. the corresponding pointwise ELPD-difference uncertainty and maximum Pareto-k diagnostic; and
3. posterior variance of ability, summarized across persons.

This LOO target is conditional on the study's observed person/item population. It is not a transport estimate for entirely new persons or new items.

A useful process channel may improve response-target held-out prediction, reduce posterior uncertainty, both, or neither. A destabilizing channel may worsen predictive performance or inflate uncertainty.

Non-additivity

The package does not sum channel Fisher information by default. Under correlated latent and item structures, information is generally not additive in the simple independent-channel sense. The ablation sequence preserves this point explicitly.

Interpretation

An incremental response-target gain supports a model-based measurement claim under the fitted assumptions. It does not by itself establish that gaze measures attention, that RT measures strategy, or that either channel is causally informative.

eyeprocess documentation built on Sept. 28, 2026, 5:08 p.m.