Principles of BehaviorSixth Edition

Richard W. MalottWestern Michigan University

Power Point by Nikki Hoffmeister

Chapter 18

Interval Schedules

What is a Fixed-Interval Schedule?

Fixed-Interval (FI) Schedule of Reinforcement:

• A reinforcer is contingent on

• the first response,

• after a fixed interval of time,

• since the last opportunity for reinforcement.

What type of responding results from an FI schedule?

Fixed-Interval Scallop:• A fixed-interval schedule often produces a

scallop – • a gradual increase in the rate of responding, • with responding occurring at a high rate • just before reinforcement is available. • No responding occurs for some time after

reinforcement.

Fixed-Interval Scallop

Joe’s Term Paper

• Sid assigned a term paper the first day of class

• Joe has 15 weeks to complete the project

• The following figure is a cumulative record of Joe’s work under this schedule

• Weeks are plotted on the abscissa

• Cumulative number of hours he worked are on the ordinate

FI Scallop of Joe’s Paper Writing

Joe’s Term Paper

• Joe spent no time preparing the paper in the first 7 weeks

• Finally, in the 8th week, he spent 5 hours preparing

• He did more the next week• And even more the next week• He spent the final week in a frenzy of long

hours in the library• This is an FI scallop, right? Wrong.

Contrasting Fixed-Interval and Term-Paper Schedules

Feature Fixed-Interval

Term-Paper

Does early responding affect anything?

No Yes

Do you get more if you work harder?

No Yes

Is the relevant response class clear?

Yes No

Are there calendars and clocks? No Yes

Is there a deadline? No Yes

Is the reinforcer too delayed? No Yes

Congress Example

• What’s the cumulative record of passing laws by the US Congress?

• A scallop; just like the pigeon pecking a key on an FI schedule.

• Members of Congress return from their annual recess (reinforcer).

• They pause for a few months, • and then they pass the first law, and gradually

increase passing laws until right before the next time for recess.

Is law-passing on an FI schedule?

• No

• In this analysis, we ask the same questions we did in the term paper example

Feature Fixed-Interval

Congress

Does early responding affect anything?

No Yes

Do you get more if you work harder?

No Yes

Is the reinforcer contingent on the final response?

Yes No

Immediate reinforcer? Yes No

Is there a deadline? No Yes

Clocks or calendars? No Yes

Other Non-Examples

• The TV Schedule

SΔ:

Calendar and clock say 9:30 AM Monday

SD:

Calendar and clock say 11:30 PM Saturday

Behavior:

You turn TV to channel 8

After:

You have no opportunity to see your favorite TV show

After:

You have opportunity to see your favorite TV show

Before:

You have no opportunity to see your favorite TV show

Analysis

• Problem 1:– You have a calendar and clock; Rudolph

doesn’t– If you didn’t, you might respond like Rudolph:

responding more and more quickly as time passed

• Problem 2:– You have a deadline; Rudolph doesn’t

Other Non-Examples

• The Paycheck

SΔ:

It has been 1 week since last paycheck

SD:

It has been 2 weeks since last paycheck

Behavior:

You pick up your paycheck

After:

You have no paycheck

After:

You have a paycheck

Before:

You have no paycheck

A Good Example

• You’re watching Seinfeld

• Commercials come on

• You switch to Jerry Springer

• But you keep switching back and forth with increasing frequency as the commercial interval wears on

• One of your flips is reinforced by Seinfeld

Superstition in the Pigeon

• Skinner put a pigeon in a Skinner box.• He placed a feeder in the box every 15

seconds, regardless of what the bird was doing.

• The first time, just prior to the feeder being presented, the pigeon had made an abrupt counter clockwise turn.

• He did the same thing the next time, right before the feeder came up.

Results

• The bird performed a stereotyped pattern of behavior: – rapid and persistent counter clockwise turns.

What is a Fixed-Time Schedule?

Fixed-Time Schedule of Reinforcer Delivery:

• A reinforcer is delivered

• after the passage of a fixed period of time,

• independently of the response.

What is Superstitious Behavior?

Superstitious Behavior:

• Behaving as if the response causes

• some specific outcome,

• when it really does not.

What is a Variable-Interval Schedule?

Variable-Interval (VI) Schedule of Reinforcement:

• A reinforcer is contingent on

• the first response

• after a variable interval of time

• since the last opportunity for reinforcement.

VI Schedules

• The opportunity for reinforcement comes as a direct function of the passage of time.

• Thus, it is a time-dependent schedule.

• The lengths of the intervals between opportunities are varied.

VI Schedules

• Although the opportunity for reinforcement occurs as a function of time alone,

• the subject must make the response

• after the interval is over for reinforcement to occur.

• Time alone will not bring about the reinforcer.

What type of responding does a VI schedule produce?

Variable-Interval Responding:

• Variable-interval schedules produce

• a moderate rate of responding,

• with almost no post-reinforcement pausing.

VI Responding

Responses can produce reinforcers in 2 ways:

1. Continuous Reinforcement: • Every response produces a reinforcer.

2. Intermittent Reinforcement: • Only some responses produce a reinforcer.

4 Classic Intermittent Schedules

Fixed Variable

Ratio Fixed-Ratio Variable-Ratio

Interval Fixed-Interval Variable-Interval

Intermittent Reinforcement & Extinction

Resistance to Extinction and Intermittent Reinforcement:

• Intermittent reinforcement

• makes the response

• more resistant to extinction

• than does continuous reinforcement.

What is Resistance to Extinction?

Resistance to Extinction:

• The number of responses

• or amount of time

• before a response extinguishes.

• The more an intermittent schedule differs from continuous reinforcement,

• the more the behavior resists extinction.

Interval Schedules vs. Time Schedules

Fixed Interval Fixed Time

Involves Time Yes Yes

Requires a Response

Yes No

Comparing & Contrasting Ratio & Variable Schedules of Reinforcement

Schedule Reinforcer Follows

Behavior

RATIO A number of responses

Fixed Ratio Fixed number of responses

After reinforcement, no responding occurs for some time. Then it

occurs at a high, steady rate until next

reinforcer.

Variable Variable number of responses

Responding occurs at a high steady rate,

with almost no post-reinforcement

pausing.

Schedule Reinforcer Follows

Behavior

INTERVAL The first response after a

time interval

Fixed Interval First response after a fixed time

interval

No response occurs immediately after

reinforcement. Then the rate increases

slowly as the interval advances (scallop).

Variable Interval

First response after a variable

time interval

A consistent and steady rate of

responding occurs, with almost no post-

reinforcement pausing.

Schedule Reinforcer Follows

Behavior

TIME A time period whether or not

there is a response

Fixed Time A fixed-time period, whether or not there is a

response

No behavior, unless superstitious

behavior resulting from accidental

reinforcement of the response of

interest.

Cumulative Recordsof 4 Schedules

Intermittent Reinforcement & Extinction

Why does intermittent reinforcement increase resistance to extinction?

• It’s easy for the rats to “tell the difference” between CRF and extinction.– During CRF, all responses produce

reinforcers– During extinction, none of them do

Also…

• It’s hard for the rats to “tell the difference” between intermittent reinforcement and extinction– During intermittent reinforcement, only an occasional

response produces a reinforcer– During extinction, none of them do

• The rats quickly discriminate between CRF and extinction

• They greatly generalize between intermittent reinforcement and extinction

Intermediate Enrichment

• Response Strength:– Response frequency– Resistance to extinction– Behavioral momentum

• Skinner rejected “response strength,” claiming it is a reification

• When you have 2 different ways of measuring the same thing, that thing is probably a reification– Those different measures may not agree

Example

• A pigeon has 2 keys in the box– One is on a CRF schedule– One is a VI 1

• According to Resistance to Extinction-Response Strength Measure:– The response on a VI 1 schedule is stronger because

it is more resistant to extinction

• But…the pigeon will most likely continue pecking the CRF key more often than the VI 1 key

On DickMalott.com

• Chapter 18 Advanced Enrichment Section– Why Do Limited Holds Work the Way They

Do?– Why Does Intermittent Reinforcement

Increase Resistance to Extinction?

Join us for Chapter 19:Concurrent Contingencies