Sensation

Sensation – Notes

  • Sensation is the process by which sensory organs (eyes, ears, nose, skin, tongue)
    detect stimuli from the environment.

  • These sensory organs convert stimuli into neural impulses
    (this process is called transduction).

  • The brain does NOT receive information directly from the outside world.

  • Instead, the brain receives electrical signals sent from the sensory organs.

  • Sensation is about detecting raw information, not interpreting it.

  • Example:

    • Light hits the eyes → eyes send neural signals → brain receives impulses

    • Sound waves hit ears → ears send neural signals → brain receives impulses

  • Sensation comes before perception

    • Sensation = detecting stimuli

    • Perception = interpreting what the stimuli mean

Psychophysics – Notes

  • Psychophysics is the study of the relationship between physical stimuli and
    our conscious experience of those stimuli.

  • It focuses on how strong a stimulus is and how we perceive it.

  • In simple terms:
    → How the physical world turns into what we experience in our mind.

  • Psychophysics explains how the senses work, not just what they detect.

  • Example:

    • Light enters the eye → converted into neural signals → brain interprets brightness

    • Sound waves hit the ear → turned into signals → brain interprets loudness

  • It looks at questions like:

    • How much light is needed to see something?

    • How loud does a sound have to be to notice it?

    • Why do two people experience the same stimulus differently?

  • Psychophysics connects:

    • Physical stimulus (light, sound, pressure)

    • Sensory response (neural signals)

    • Perception (what you consciously experience)

Difference Threshold / Just Noticeable Difference (JND) – Notes

  • Difference threshold and Just Noticeable Difference (JND) mean the same thing.

  • JND = the smallest change in a stimulus that a person can detect.

  • It focuses on noticing a difference, not just detecting the stimulus.

  • Question it answers:
    → How much must a stimulus change for me to notice it?

Example (Shower Example)

  • Water is too hot when you enter the shower.

  • You turn the hot water down slightly.

  • At some point, you notice the temperature change.

  • That exact point is the JND.

Key Definition (Test-ready)

The Just Noticeable Difference is the smallest amount of change in a stimulus that can be detected.

Important Tip

  • Absolute threshold = noticing something

  • Difference threshold (JND) = noticing a change

Sensory Adaptation – Notes

  • Sensory adaptation happens when sensory receptors become less sensitive to a constant stimulus over time.

  • The stimulus does not change, but your response to it does.

  • This happens because receptor cells reduce their firing after being constantly stimulated.

Shower Example

  • When you first get into the shower, the water feels warm.

  • After a few minutes, the same water feels cooler.

  • The temperature didn’t change.

  • Your skin’s temperature receptors adapted.

  • If you turn the hot water up:

    • The receptors are stimulated again

    • The water feels warm once more

Why Sensory Adaptation Happens

  • Helps you focus on new or changing stimuli

  • Prevents overload from constant stimulation

Quick Test Definition

Sensory adaptation is the decreased sensitivity to a constant stimulus over time.

Signal-Detection Theory – Notes

  • Signal-detection theory explains how and why we detect certain stimuli and miss others.

  • It says detecting a stimulus depends on more than just the stimulus itself.

Three Factors That Affect Detection

  1. Characteristics of the stimulus

    • Strength, intensity, clarity

    • Example: a loud sound is easier to detect than a quiet one

  2. Background noise

    • Other stimuli in the environment

    • More noise = harder to detect the signal

  3. Characteristics of the detector (the person)

    • Attention, expectations, fatigue, motivation, experience

    • Example: you’re more likely to hear your phone if you’re expecting a call

Key Idea

  • Detection is not automatic

  • It depends on both the environment and the person

Quick Test Definition

Signal-detection theory explains how stimulus detection depends on the stimulus, background noise, and the individual.

Signal Detection – Doorbell Example

  • Signal: the doorbell ringing

  • Noise: music, talking, and sounds from the party

  • Detector: your hearing (the person)

  • When the party is loud, the background noise makes it harder to hear the doorbell.

  • As you start expecting the food to arrive, you pay more attention.

  • Because of this expectation, your ability to detect the doorbell increases, even though the noise stays the same.

Key Idea

  • Detection depends on:

    • the signal

    • the noise

    • the person’s attention and expectations

Quick Test Connection

Signal-detection theory shows that expectations and attention affect whether a stimulus is noticed.

Characteristics in Signal Detection – Notes

In signal-detection theory, whether a stimulus is detected depends on three elements, each with its own characteristics.

1. Characteristics of the Stimulus

  • Intensity

    • How strong the stimulus is

    • Example: louder sound, brighter light

  • Contrast

    • How much the stimulus stands out from its surroundings

    • Example: a bright light in a dark room

2. Characteristics of Background “Noise”

  • Level of noise

    • How much other stimulation is present

    • Example: loud party vs. quiet room

  • Variations in noise level

    • Changes in background noise

    • Example: music getting louder or quieter

3. Characteristics of the Detector (Person)

  • Expectations

    • What you think will happen

    • Example: expecting the doorbell to ring

  • Physical factors

    • Fatigue, health, sensory ability

  • Social factors

    • Peer influence, situation, surroundings

  • Emotional factors

    • Stress, anxiety, mood

  • Cultural factors

    • Past experiences and learned meanings

Quick Summary

Detecting a signal depends on the stimulus itself, the background noise, and the person detecting it.

Characteristics in Signal Detection – Notes

In signal-detection theory, whether a stimulus is detected depends on three elements, each with its own characteristics.

1. Characteristics of the Stimulus

  • Intensity

    • How strong the stimulus is

    • Example: louder sound, brighter light

  • Contrast

    • How much the stimulus stands out from its surroundings

    • Example: a bright light in a dark room

2. Characteristics of Background “Noise”

  • Level of noise

    • How much other stimulation is present

    • Example: loud party vs. quiet room

  • Variations in noise level

    • Changes in background noise

    • Example: music getting louder or quieter

3. Characteristics of the Detector (Person)

  • Expectations

    • What you think will happen

    • Example: expecting the doorbell to ring

  • Physical factors

    • Fatigue, health, sensory ability

  • Social factors

    • Peer influence, situation, surroundings

  • Emotional factors

    • Stress, anxiety, mood

  • Cultural factors

    • Past experiences and learned meanings

Quick Summary

Detecting a signal depends on the stimulus itself, the background noise, and the person detecting it.

Transduction – Notes

  • Transduction is the process by which sensory receptors convert raw stimuli into neural (nerve) impulses.

  • It happens after the stimulus is detected by the sensory organs.

  • The brain cannot understand raw stimuli (light, sound, pressure) directly.

  • Transduction changes physical energy into a language the brain understands.

Vision Example

  • Light enters the eye.

  • Photoreceptor cells in the retina detect the light.

  • The light is converted into neural impulses.

  • These impulses travel to the visual cortex.

  • You experience the sensation of light.

Key Phrase to Remember

Transduction = converting stimulus energy into neural signals.

Quick Test Definition

Transduction is the conversion of sensory stimuli into neural impulses.

Sensation

The process by which sensory organs detect stimuli from the environment and send raw information to the brain as neural impulses.

Psychophysics

The study of the relationship between physical stimuli and our conscious experience of those stimuli.

Receptor Cells

Specialized cells in the sensory organs that detect specific types of stimuli (light, sound, pressure, chemicals) and begin the sensory process.

Transduction

The process by which receptor cells convert sensory stimuli into neural impulses that the brain can interpret.

Absolute Threshold

The minimum amount of stimulation needed to detect a stimulus 50% of the time.

Difference Threshold (Just Noticeable Difference – JND)

The smallest change in a stimulus that can be detected 50% of the time.

Sensory Adaptation

The decreased sensitivity to a constant stimulus over time.

Signal Detection Theory

A theory explaining that detecting a stimulus depends on the stimulus itself, background noise, and the individual’s expectations and condition.

One-Line Memory Tip

  • Sensation = detect

  • Psychophysics = measure

  • Transduction = convert

  • Thresholds = limits

  • Adaptation = adjust

  • Signal detection = context + attention