Interoceptive Accuracy Scale (IAS)

Developed by Murphy, Brewer, Plans, Khalsa, Catmur & Bird in Murphy et al. (2020) to occupy a quadrant of their 2×2 model of interoceptive measurement that had almost nothing in it: self-reported accuracy.

Why the quadrant was empty, and why it mattered

The Murphy–Catmur–Bird model crosses what is measured (accuracy of perception vs the body being the object of attention) with how (objective performance vs self-reported belief). Three quadrants were well populated — objective accuracy by the heartbeat tasks, self-reported attention by the BPQ and MAIA Noticing, objective attention (thinly) by experience-sampling. Self-reported accuracy had one instrument, the Interoceptive Confusion Questionnaire (Brewer, Cook & Bird 2016), with imperfect psychometrics, plus post-task confidence ratings — which are state-dependent and confined to whatever channel the task uses.

The gap was not cosmetic. Without a trait accuracy-belief measure you cannot test whether the accuracy/attention distinction is real, because every available self-report is on the attention side, so every self-report↔task comparison in the literature is confounded with the what axis. That confound is the wiki’s most-repeated null.

The items, and what they are trying to avoid

Every item takes the same frame — “I can always accurately perceive when I…” — across heartbeat, hunger, breathing, thirst, urination, defecation, taste, vomiting, sneezing, coughing, temperature, sexual arousal, passing wind, burping, muscle soreness, bruising, pain, low blood sugar, affective touch, tickle and itch.

Two design decisions are worth recording, because they are what distinguish it from the MAIA:

• No attention items. Nothing asks how often the respondent notices, monitors or listens to the body. The deployed-attention split is built into the instrument rather than discovered in it afterwards.
• No worked examples inside the items. Unlike the ICQ (“I frequently forget to eat”), IAS items stay abstract. The stated rationale is that an individual’s difficulty perceiving hunger may not manifest as the specific behaviour an example names — it may show up as overeating rather than as forgetting to eat.

The instruction to rate perception without external cues is doing real work: it is the only thing separating the IAS from a measure of how well a person infers their internal states by any available route, which is a different construct entirely.

Its one genuine claim on the wiki

The IAS is the only self-report instrument here that has been shown to correlate with objective interoceptive performance. That result is small (r ≈ .27–.34), doubly underpowered, and cardiac — but it is selective in a way that matters more than its size: in the same participants and the same sessions, the BPQ correlated with the same task at r = .091 and below.

Read across interoceptive-taxonomy, that is the taxonomies’ central distinction doing empirical work for once. Read against interoceptive-sensitivity, it says the wiki’s accumulated “sensibility does not predict accuracy” nulls were mostly measured with attention scales, and the claim needs restating with the what axis held fixed.

Adoption

Used by Ventura-Bort, Wendt & Weymar (2021), where it loaded at +.79 on their “Sensibility” (believed-accuracy) component alongside reversed TAS-20 and MAIA Trusting — independent confirmation of where the instrument sits, from a lab with no stake in the 2×2.