Score NOR exploration with the live keyboard scoring pad or enter pre-timed totals. Get Discrimination Index, Preference Index, and group comparisons with error bars.
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Session Time
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Familiar (F)
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Novel (N)
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Press Start, then hold F for familiar and N for novel object exploration
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If all animals in the "novel" condition see the same physical object, apparent recognition memory could actually be spontaneous object preference. Counterbalance so that each object serves as novel for half of the subjects within each group.
DI is undefined when total exploration equals zero and extremely noisy when total exploration is very low. Most labs require at least 20 seconds of total exploration during the test phase. Animals below this threshold should be excluded and reported as such in your methods.
Insufficient familiarization leads to weak encoding, resulting in chance-level DI even in control animals. Ensure animals actually explore both objects during the sample phase — do not assume that placing an animal in the arena guarantees adequate encoding.
A 1-hour ITI tests short-term memory, a 24-hour ITI tests long-term memory. These recruit different neural substrates and pharmacology. Be explicit about your ITI and what memory process you intend to assess.
A DI of 0.6 based on 50 seconds of total exploration is far more reliable than a DI of 0.6 based on 8 seconds. Sedating drugs can reduce overall exploration, making DI unreliable even if technically computable. Always report total exploration time so readers can assess data quality.
Computes Discrimination Index DI = (N-F)/(N+F) and Preference Index PI = N/(N+F) from exploration times. Keyboard scoring mode uses press-and-hold timing with millisecond resolution via browser performance API. Group statistics use sample standard deviation (n-1 denominator) for SEM. All computation is client-side — no data leaves your browser.
Last validated 2026-04-05. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience NOR Discrimination Index Calculator (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/novel-object-recognition-discrimination-index
This tool performs mathematical calculations on user-provided data. It does not replace scientific judgment regarding experimental design, exclusion criteria, or statistical analysis.
The Novel Object Recognition (NOR) test was introduced by Ennaceur and Delacour in 1988 as a one-trial learning task that exploits the innate tendency of rodents to explore novelty. In the standard protocol, an animal is first habituated to an open-field arena (habituation phase), then allowed to explore two identical objects during a familiarization (sample) phase. After an inter-trial interval, the animal is returned to the arena where one of the familiar objects has been replaced with a novel object (test phase). Animals with intact recognition memory spend significantly more time investigating the novel object. The NOR test has become one of the most widely used assays in behavioral neuroscience because it is simple, does not require food or water deprivation, avoids aversive stimuli, and is sensitive to hippocampal and perirhinal cortex lesions as well as pharmacological manipulations affecting memory.
The Discrimination Index (DI) quantifies how much an animal prefers the novel object relative to total exploration. It is computed as DI = (novel exploration time - familiar exploration time) / (novel exploration time + familiar exploration time). DI = 0 means equal exploration of both objects (chance performance); DI > 0 indicates novel object preference (intact recognition); DI < 0 indicates familiar object preference (rare, may indicate anxiety or procedural issues). A closely related measure is the Preference Index (PI = novel / total), which ranges from 0 to 1 with 0.5 as chance. Both metrics normalize for individual differences in overall activity levels — an important advantage over raw exploration times. When reporting results, provide both DI (or PI) and total exploration time, because very low total exploration makes the index unreliable. Group data should be reported as mean SEM with individual data points visible.
Object selection is the most common source of confounds in NOR studies. Objects must be counterbalanced across animals so that every object serves as both novel and familiar for different subjects — this controls for spontaneous object preference. Objects should differ in shape and color but be similar in size and complexity. Avoid objects with strong odors, sharp edges, or surfaces that allow climbing. The arena should be opaque, well-lit (15-20 lux for standard NOR; dim red light for anxiety-sensitive strains), and cleaned with 70% ethanol or a mild detergent between trials. Place objects equidistant from the walls and from each other. Video-record all sessions and define exploration operationally (e.g., nose directed toward object within 2 cm, excluding sitting on or leaning against the object). Use multiple independent scorers or automated tracking to establish inter-rater reliability. The familiarization phase should provide sufficient exposure (typically 5-10 minutes with two identical copies of the to-be-familiar object) and the test phase should be 5 minutes unless your protocol specifies otherwise.
Complete NOR arena with standardized object sets for recognition memory testing
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