Sensation and Perception

Introduction

What is a sensation? Usually refers to the physical stimulus in

the environment (light, sound waves).

We convert physical energy from the world into neural energy our brains can process.

What is perception? Refers to how we interpret the stimulus

information our nervous system takes in & processes.

Does perception equal physical reality?

What do you think????

The Perceptual Process

Step 1: Distal Stimulus (stimulus at a distance: me, a friend).

Step 2: Proximal Stimulus (stimulus in proximity to your receptors).

Step 3: Transduction (process by which physical energy is transformed into neural energy that can be processed).

Step 4: Neural Processing (neural energy is processed by brain).

Step 5: Perception (Neural information is interpreted into a percept).

Step 6: Recognition (Do I recognize the person or object?).

Step 7: Action (Will you go over to the object?).

Three approaches to studying perception 1. Stimulus-Perception Relationship- the

relationship between the physical stimulus & what we perceive.

2. Stimulus-Physiology Relationship – the connection between stimuli & nerve firing.

3. Physiology-Perception Relationship – how does neural processing in the brain effect perception.

What is the most rudimentary concept in perception?

Stimulus detection

How do we detect a stimulus in the environment?

We look for the least amount of stimulus energy needed in order for a stimulus to be detected.

The Absolute threshold is the smallest amount of energy required to detect a stimulus (50% of the time).

E.g., How many photons of light (light particles) are needed for you to detect a light source?)

Myths in measuring thresholds 1. People can accurately tell us when they detected a

stimulus.

-Not true, people are often unsure of what they’ve perceived.

2. The subject shouldn’t report a response unless a signal was presented.

No, random neural firing might make them think something happened when it didn’t. You think you hear the phone ringing while taking a shower.

Classical Psychophysical Methods for measuring thresholds.

1. Method of Limits – the S is presented with stimuli that either increase in intensity (ascending series) or systematically decrease in intensity (descending series) until the S reports that a stimulus was detected.

The point at which the S reports no longer being able to detect the signal is called the “crossover point.”

Method of Limits Advantages 1. Its quick & easy to administer

Disadvantages 2. Habituation—S tend to make the same response.

3. Anticipation-the S anticipates their response before seeing or hearing the stimulus.

2. The Method of Adjustment

The stimulus is slowly changed as the S adjusts the stimulus intensity until the stimulus is either no longer detectable or detectable.

Method of adjustment

Advantages: 1. It’s quick to do. 2. The S is an active participant, so the experiment is

more interesting for them.

Disadvantages: 1. Ss may crank up the intensity too high &

desensitize their sensory systems. 2. Ss have knowledge about the stimulus, which may

change thresholds.

3. Method of Constant Stimuli

The experimenter picks a range of intensities & randomizes the order of the stimuli.

Advantages 1. Removes anticipation bias which reduces bias

in the threshold measurement.

Disadvantages 1. This method is slow & time consuming. 2. The S may become easily bored.