Fixed Interval
Overview
The fixed interval (FI) schedule reinforces the first response emitted after a fixed period of time has elapsed since the last reinforcer. For example, under FI30s, the first lever press after 30 seconds earns a pellet, regardless of how many responses occurred during the interval. FI schedules produce a characteristic "scallop" pattern: low response rates immediately after reinforcement, accelerating as the interval elapses.
FI schedules are fundamental to the study of temporal control of behavior. Animals learn to estimate the interval duration and adjust their response rate accordingly — a process dependent on dopaminergic timing circuits in the striatum and prefrontal cortex. The FI scallop provides a sensitive assay for drugs affecting time perception, attention, and motivation.
ConductMaze automates FI scheduling with precise interval timing, real-time cumulative record generation, and automated scallop analysis. The software calculates quarter-life and index-of-curvature metrics that quantify temporal discrimination, and supports within-session interval changes for temporal generalization studies.
Trial Flow
Session Start
House light ON, levers extended, first interval begins
Interval Timer
Fixed time period elapses; responses recorded but not reinforced
Interval Elapsed
Has the programmed interval duration passed?
First Response
First active press after interval ends
Reinforcer Delivery
Pellet dispensed, cue light activated, new interval starts
Session Limit Check
Max reinforcers or time limit reached?
Session End
Levers retracted, data saved
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Interval Duration | seconds | 30 | Fixed time period between reinforcement availability (e.g., FI30, FI60, FI120) |
| Max Reinforcers | integer | 40 | Maximum reinforcers before session ends |
| Max Session Time | seconds | 3600 | Absolute session time limit |
| Active Lever Side | enum | Right | Which lever is reinforced |
| Cue Light Duration | seconds | 3 | Duration of cue light paired with reinforcer |
| Reinforcer Type | enum | Sucrose Pellet | Type of reinforcement delivered |
| Limited Hold | seconds | 0 | Time window after interval for valid response (0 = unlimited) |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Total Active Presses | count | Total presses on the active lever across the session |
| Total Inactive Presses | count | Total presses on the inactive lever |
| Reinforcers Earned | count | Total reinforcers delivered |
| Response Rate | presses/min | Mean active lever press rate |
| Quarter Life | seconds | Time to emit 25% of interval responses — measures temporal discrimination |
| Index of Curvature | index | Quantification of FI scallop shape (0 = flat, 1 = perfect scallop) |
| Post-Reinforcement Pause | seconds | Mean pause after reinforcer delivery before next response |
Sample Data
| Interval | Active_Presses | Inactive_Presses | PRP_s | Quarter_Life_s | Curvature_Index |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Temporal cognition — FI scallops as a behavioral assay for interval timing ability
- 2Psychopharmacology — detecting drug effects on time perception (e.g., dopamine agonists flatten scallops)
- 3Schedule comparison — contrasting FI and FT (fixed time, non-contingent) to dissociate operant vs. Pavlovian processes
- 4Behavioral baseline — stable FI performance for within-subject drug challenge designs
- 5Developmental neuroscience — tracking maturation of temporal control from juvenile to adult
Related Protocols
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