Visual Water Task
Overview
The visual water task, developed by Prusky, West, and Douglas (2000), is the definitive behavioral method for measuring visual acuity and pattern discrimination in freely swimming mice and rats. The apparatus consists of a trapezoidal-shaped water tank with a Y-shaped choice point at one end, where two computer monitors display visual stimuli — typically sinusoidal gratings of varying spatial frequency. A submerged escape platform is positioned directly below the monitor displaying the rewarded stimulus (S+), while the other arm (S−) has no platform. The animal learns to swim toward the correct visual pattern to escape the water, and by progressively increasing the spatial frequency of the gratings, the experimenter determines the animal's visual acuity threshold — the highest spatial frequency at which the animal can still discriminate S+ from S−.
Each trial begins with the animal placed at the wide end of the trapezoid, facing the two stimulus monitors. The animal swims toward the choice point and selects one arm by crossing an invisible decision line. If the animal chooses the S+ arm, it finds the escape platform and is removed to a dry holding cage. If it chooses the S− arm, it encounters a barrier, must turn around, and is guided or allowed to self-correct. Trials are organized into blocks of 10, and performance at each spatial frequency is assessed against a criterion of 70% or 80% correct. The staircase procedure increases spatial frequency when criterion is met and decreases it after failures, converging on the acuity threshold. For pattern discrimination variants, different shapes, orientations, or contrast levels replace spatial frequency as the independent variable.
ConductMaze controls both stimulus monitors via a dedicated display controller, presenting gratings with precisely calibrated spatial frequency, contrast, orientation, and phase. The software detects the animal's arm choice using infrared beam-break sensors at the decision line, automatically logs trial outcomes, and implements the staircase procedure in real time. Platform access is gated by a motorized barrier that opens only in the correct arm, and the software computes psychometric functions, acuity thresholds, and discrimination indices across sessions.
Trial Flow
Stimulus Display
S+ and S− gratings rendered on left/right monitors, side randomized
Animal Release
Subject placed at start position, begins swimming toward choice point
Arm Choice Detection
IR sensor at decision line registers which arm the animal enters
Choice Evaluation
Did the animal enter the S+ arm (correct) or S− arm (incorrect)?
Platform Access
Correct: platform accessible, animal escapes. Incorrect: barrier blocks, 10s penalty
Staircase Update
Update running accuracy; adjust spatial frequency if criterion met or failed
Block Completion Check
Trial block complete? Assess threshold convergence
Session End
Record acuity threshold, save psychometric data
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Starting Spatial Frequency | float | 0.10 | Initial grating spatial frequency in cycles per degree (easy, large stripes) |
| Frequency Step Size | float | 0.03 | Increment/decrement in cycles/degree per staircase step |
| Criterion Performance | float | 0.70 | Proportion correct required to advance spatial frequency (typically 0.70 or 0.80) |
| Trials per Block | integer | 10 | Number of trials per spatial frequency level before criterion assessment |
| Stimulus Contrast | float | 1.0 | Michelson contrast of the grating stimulus (0.0 to 1.0) |
| Stimulus Type | enum | Sine Grating | Visual stimulus category (Sine Grating, Square Grating, Shape Discrimination, Contrast) |
| Max Trial Duration | seconds | 60 | Maximum time allowed per trial before it is scored as incomplete |
| Water Temperature | float | 23.0 | Water temperature in °C (maintained for consistent swim motivation) |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Visual Acuity Threshold | cycles/degree | Highest spatial frequency at which performance meets criterion — primary measure of visual resolution |
| Percent Correct | % | Proportion of correct arm choices per trial block |
| Discrimination Index | ratio | (Correct − Incorrect) / Total trials — strength of pattern discrimination |
| Swim Time | seconds | Time from release to arm choice — swim speed and decision latency |
| Self-Correction Rate | % | Proportion of incorrect trials where the animal reversed and found the correct arm |
| Trials to Criterion | count | Number of trials required to reach criterion at each spatial frequency |
| Contrast Sensitivity | 1/contrast | Reciprocal of the minimum contrast at which discrimination is maintained |
Sample Data
| Subject | Group | Spatial_Freq_cpd | Pct_Correct | Swim_Time_s | Trials_to_Criterion | Threshold_cpd |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Retinal degeneration phenotyping — measuring progressive visual acuity loss in rd1, rd10, and other retinal dystrophy mouse models
- 2Optic nerve and glaucoma research — quantifying functional visual deficits following elevated intraocular pressure or optic nerve crush
- 3Gene therapy efficacy — assessing visual function rescue after AAV-mediated gene delivery to photoreceptors or retinal ganglion cells
- 4Cortical visual processing — evaluating visual discrimination after targeted lesions to primary visual cortex or higher visual areas
- 5Pharmacological neuroprotection — screening compounds that preserve visual function in neurodegenerative disease models
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