What type of reinforcement schedule is it, when reinforcement is provided to…

Reinforcement schedules in operant conditioning are classified along two independent axes: what triggers the reinforcement — a ratio schedule ties it to the number of responses, an interval schedule ties it to elapsed time — and whether that trigger stays fixed (a constant, predictable value) or varies (changes unpredictably around an average). Crossing these two axes produces four schedules: fixed ratio, variable ratio, fixed interval, and variable interval.

The stem states that reinforcement is given only after a certain number of responses occurs. "A certain number" places the trigger on the ratio axis (a response count, not a time span) and describes that count as fixed rather than changing, which places it on the fixed axis. Combining a ratio trigger with a fixed value identifies the schedule as fixed ratio.

• Fixed ratio: reinforcement follows a constant, pre-set number of responses in every cycle (for example, always the 5th response).

• Variable ratio: reinforcement follows a number of responses that changes from cycle to cycle, averaging around a set value rather than staying constant.

• Fixed interval: reinforcement becomes available after a constant span of elapsed time, regardless of how many responses occur within that span.

• Variable interval: reinforcement becomes available after a span of elapsed time that changes from cycle to cycle around an average, also independent of the response count.

Cross-checking against the stem, in order:

1. The trigger described is a response count, not elapsed time — this rules out both interval schedules, since they depend on time rather than count.

2. That count is described as certain/fixed rather than changing — this rules out the variable-ratio schedule, whose count changes cycle to cycle.

3. Only the fixed ratio schedule matches both properties.