Information Processing

metaphor

The structure and function of one thing is used to roughly describe another thing

Mental Chronometry

measuring how long mental processes take by looking at reaction time (RT).

Hermann von Hemholtz

• first to measure nerve conduction in a frog’s sciatic nerve

• On average he found 24.6-38.4 meters per second

• Measured time taken by distinct mental operations
  

A — Simple RT

one stimulus and one response
no choice, just detect and react

Measures: Basic physiological RT (sensory → motor, no decision needed)

Complexity: Lowest

B — Go / No-Go

Respond ONLY to a designated stimulus; withhold for others

Measures: Adds stimulus IDENTIFICATION time

Complexity: Medium

C — Choice RT

Multiple stimuli, each with its own unique response

Measures: Adds RESPONSE SELECTION time on top of identification

Complexity: Highest

Donders' Subtractive Logic

comparing reaction times from different tasks to estimate how long one mental process takes.
RT of harder MINUS Rt of easier = time for extra mental step

Limitations of Subtractive Logic

• Assumes pure insertion (stages don't overlap or interact)

• Real stages may run in parallel — violating this assumption

• Tasks may differ in more than one stage

The Psychological Refractory Period (PRP) Effect

• When two stimuli appear in rapid succession, the response to the SECOND stimulus is slower

• This delay is called the Psychological Refractory Period (Welford, 1952)

• The effect is stronger when the gap (SOA) between stimuli is shorter

Information Theory

Claude Shannon (1916-2001)

• Mathematician not psychologist

• Developed tools for telecommunications, like digital circuit theory (1937)

the more uncertain you are before something happens, the more information you gain when you find out what happened

Entropy (H)

Measure of uncertainty or chaos in a set of messages/system

Bits

Unit of information; number of binary yes/no questions needed to identify a message

Channel Capacity

the maximum amount of information a person/system can process accurately at one time.

Low H (Low Entropy)

Sequence is highly predictable Little "surprise" in messages

Example: A book that repeats the letter A on every page → you always know what comes next → H ≈ 0

High H (High Entropy)

Sequence is unpredictable Messages carry a lot of "information"

Example: A book with completely random letter sequences → maximum uncertainty → H is highest

Understanding Bits of Information

• Each time you double the alternatives, bits increase by just 1 (logarithmic growth)

• This means going from 4 → 8 options adds only 1 bit, not double the information

• Cognitive psychology adopted bits to measure 'how much stimulus information' people proces

Why Does More Choice = Slower Response?

When items are presented randomly and equally often, # of alternatives and bits are perfectly confounded!

You cannot tell whether RT increases because of: • More alternatives OR • More information (bits)

The Set-Size Effect

In choice RT tasks, mean RT rises as the number of stimuli alternatives increases

Number of Alternatives

More items = more possibilities to check through. Response slows because there are simply more things to discriminate

Amount of Information

People are actually sensitive to PREDICTABILITY. If items aren't equally likely, unpredictable items slow you down

The Hick-Hyman Law

Predictable stimuli → faster responses

Unpredictable stimuli → slower responses

• Reaction time increases as the amount of information or uncertainty increases; people respond to predictability, not just stimulus count
  

Why the Hick-Hyman Law Mattered

• Challenged behaviorism: responses don't just depend on the immediate stimulus — past context matters

• People are sensitive to the relative predictability of ALL alternatives, not just what's in front of them

• Suggested cognition involves processing probability and prediction — a deeply cognitive, not reflexive, process