Sensation

Overview How is perception different from sensation? What is psychophysics? What do sense organs do? How does vision work? How does this compare to other senses?

How is Perception Different From Sensation? Sensation refers to stimulation of sense organs Perception is the selection and organization of sensory information by the brain

What is Psychophysics? Study of the relationship between physical properties and psychological experience

Signal Detection Theory HitFalse Alarm Miss Correct Rejection Stimulus Present? YesNo Response No Yes

Sensitivity Sensitivity is a measure of how well the observer can detect stimuli  Sensory ability of observer  Signal to noise ratio Higher sensitivity means:  Higher hit rate  Lower false alarm rate

Criterion The criterion is the level of intensity at which the observer chooses to switch from “No” to “Yes” responses How intense does the stimulus have to be for the observer to respond “Yes?” Affected by:  Payoff for hits  Penalty for false alarms  Probability of stimulus occurring

What Do Sense Organs Do? Each sense organ responds to a particular type of environmental input Sense organs change input from the environment into a pattern of neural signals This process is called transduction The brain deals only with neural signals

Visible Light Electromagnetic energy Visible light is a small part of the spectrum  Wavelength  Intensity

The Work of The Eyes The cornea is responsible for much of the focusing power of the eye Light is admitted into the eye through the pupil The iris controls the size of the pupil The lens allows for adjustable focus Light is focused onto the retina

The Retina The retina is the back lining of the eye Contains photoreceptors (rods & cones) Photoreceptors contain photopigment molecules Light causes a chemical change in the photopigment The chemical change results in graded potentials

Message to the Brain Messages from the graded potentials go through two other layers of cells in the retina Axons of ganglion cells form the optic nerve Where the optic nerve exits from the retina, no photoreceptors exist; this is the blind spot Information from the right visual field is sent to the left hemisphere of the brain, and vice versa

NOT a Problem for the Brain The images on the retinas are upside down and backwards The brain does NOT have to turn these images around Why not?

How Does Vision Compare to Other Senses? All senses work by transducing environmental input Sound energy is transduced by receptors in the cochlea (inner ear) Receptors in the nasal cavity and mouth respond to various chemical substances Receptors in the skin respond to mechanical energy