Prices

An associative memory task with a learning and a recognition phase. Participants are shown item–price pairs and asked to remember them, then tested on which price was paired with each item. Prices are localized to the participant's currency.

• Duration: ~120 s
• Source: ARC · Nicosia et al., 2022 — custom implementation
• Launch URL: https://andreifoldes.github.io/m2c2-assessments/assessments/prices/

Running with or without images

Study launches (token, callback, or embed=1) are word-only by default: each item is shown as its name plus a price. Add images=1 (or images=true) to show a photograph of the item above the name during the tutorial example and the learning phase. The public GitHub Pages demo (no token / callback / embed) loads photographs automatically; pass images=0 to force word-only. The recognition phase stays word-only in both modes, so the test remains of the item–price association rather than picture recognition.

Photographs are prefetched as data URLs before the session starts, so trial-onset timing is not affected by network latency. If images=1 is set but no photographs can be loaded (missing host, CORS failure, empty directory), the task logs a warning and runs in word-only mode. Trial data include images_enabled so analyses can distinguish the two modes.

The photographs are not redistributed in this repository. Host them privately (same pattern as FNAME-Pairs: an unguessable path on a host you control, with cross-origin GET allowed) and pass the host via stimuli_base_url. Locally, if the gitignored files are present under assessments/prices/assets/prices/images/, ?images=1 works without that parameter. A deploy script at assessments/prices/tools/deploy_stimuli.sh publishes the files to a private-by-obscurity Netlify site.

How the photographs were selected

Item photographs come from the THINGS database:

Hebart, M. N., Dickter, A. H., Kidder, A., Kwok, W. Y., Corriveau, A., Van Wicklin, C., & Baker, C. I. (2019). THINGS: A database of 1,854 object concepts and 26,170 naturalistic object images. PLOS ONE, 14(10), e0223792. doi:10.1371/journal.pone.0223792

Stoinski, L. M., Perkuhn, J., & Hebart, M. N. (2024). THINGSplus: New norms and metadata for the THINGS database of 1854 object concepts and 26,107 natural object images. Behavior Research Methods, 56(3), 1583–1603. doi:10.3758/s13428-023-02110-8

Each of the 40 pool items (plus the tutorial example, Bananas) is mapped to a THINGS concept. Candidate photographs for that concept were ranked on THINGSplus nameability together with image-level recognizability and memorability; the rank-1 (best-pick) image is the one the task loads. A few items map to a nearby concept rather than an identical label: Aspirin → pill, Lotion → cream, Vegetable Oil → oil, Light Bulb → lightbulb.

That choice followed a source audit of the item pool against four open-licensed emoji families (OpenMoji, Twemoji, Noto Emoji, Fluent Emoji), the THINGSplus CC0 one-per-concept photographs, the THINGS best-picks, and MultiPic line drawings. Emoji coverage was incomplete and some mappings collided (for example Celery and Spinach both mapped to "leafy green"). MultiPic supermarket coverage was thin. THINGS best-picks uniquely covered every pool item with a distinct, nameable photograph, so they were selected.

Example URL commands

# Plain launch (debug mode: results shown on-screen)
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/

# Suppress the completion screen
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/?show_end_screen=false

# With camera recording
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/?webcam=1

# With eye tracking
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/?webgazer=1

# Customized assessment parameters (values shown are the defaults)
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/?number_of_items=10&learning_duration_ms=3000&show_good_price_question=true

# With item photographs (THINGS best-picks; recognition phase stays word-only)
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/?images=1&stimuli_base_url=<STIMULI_BASE_URL>

# Production: submit results to your server
https://andreifoldes.github.io/m2c2-assessments/assessments/prices/?token=<TOKEN>&callback_url=<CALLBACK_URL>

Session parameters

Handled by the launch wrapper (results submission and optional sensors), not by the assessment itself.

Parameter	Type	Default	Description
callback_url	string	—	URL to POST results to when the assessment ends.
embed	string	—	Set to 1 for embedded mode (e.g. an ESMira PWA iframe): on completion, results are posted to the parent window via postMessage instead of an HTTP callback.
images	string	—	Set to 1 or true to show an item photograph above each item during the tutorial example and the learning phase (Prices). The recognition phase stays word-only. If photographs cannot be loaded, the task falls back to word-only mode.
light	string	—	Set to 1 or true to enable ambient light sensing (where the browser supports the AmbientLightSensor API). Participants see a consent prompt; lux readings are recorded during the task and exported at session end.
pid	string	—	Optional participant identifier. Echoed verbatim into the results: top-level pid next to token in the callback POST, inside data, and in the embed-mode postMessage. Useful when the callback endpoint does not mint per-participant tokens, or to link multi-session designs (e.g. FNAME-Pairs learning vs. delayed) from the URL alone.
recognition_feedback	string	—	Set to 1 or true to color the chosen recognition button green/red by accuracy (Prices). By default the selection is highlighted in a neutral color, giving no accuracy feedback.
show_end_screen	string	true	Set to false or 0 to suppress the green "Assessment Complete" screen after results are submitted. A Telegram WebView closes immediately instead of showing the confirmation.
stimuli_base_url	string	assets/prices/images/	Base URL for the item photographs. Only used when images=1. The THINGS images are fair-use research stimuli hosted outside this repository (see Running with or without images).
token	string	—	Authentication token for results submission. When absent (along with callback_url), the assessment runs in debug mode and displays results on-screen instead of submitting them.
tutorial	string	true	Set to false or 0 to skip the tutorial screens (alias for the show_tutorial assessment parameter).
webcam	string	—	Set to 1 or true to enable optional camera recording. Participants see a consent prompt; if they accept, the front camera records and the video is saved locally to their device at session end.
webgazer	string	—	Set to 1 or true to enable browser-based eye tracking via WebGazer.js. Participants see a consent prompt, then a 5-point gaze calibration. Gaze coordinates are recorded throughout the task and exported as a CSV file at session end. Can be combined with webcam=1.

Assessment parameters

Parameters marked URL can be set as URL query parameters; the rest are fixed deployment defaults.

Parameter	Type	Default	URL	Description
number_of_items	number	10	✅	Number of item-price pairs per session
learning_duration_ms	number	3000	✅	Display duration per item in learning phase (ms)
show_good_price_question	boolean	true	✅	Show 'Is this a good price?' question during learning phase
show_tutorial	boolean	true	✅	Show the tutorial before the test
show_images	boolean	false	—	Show item photographs in the tutorial and learning phases (enabled via the images=1 URL param)
item_images	string	{}	—	JSON map of item name to image data URL (set by index.js after image prefetch)
show_recognition_feedback	boolean	false	—	Color the chosen recognition button green/red by accuracy. Off by default: the selection is highlighted neutrally instead
min_price_distance_usd	number	3	✅	Minimum separation between correct price and distractor, expressed in USD. Automatically converted to the local currency equivalent using approximate exchange rates.
locale	string	en-GB	✅	BCP 47 locale tag (e.g. 'en-GB', 'fr-FR'). Set to 'auto' to detect from the browser.
currency	string	GBP	✅	ISO 4217 currency code (e.g. 'GBP', 'EUR'). Set to 'auto' to infer from locale.
excluded_items	string	""	✅	Comma-separated item names to exclude from this session. Use for within-day no-repeat rule (Rule 7).
used_item_prices	string	{}	✅	JSON object mapping item names to arrays of previously used prices. E.g. '{"Almonds":[3.27,5.82],"Cereal":[7.63]}'. Prevents re-presenting the same item-price pair (Rule 8).
show_trials_complete_scene	boolean	false (site override; package default true)	—	After the final trial, should a completion scene be shown? Otherwise, the game will immediately end.

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Generated from assessments/prices/prices.js and assessments/prices/index.js. Do not edit by hand.