2 Transduction: conversion of one form of energy into another In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brains can interpret When the appropriate stimulus reaches the sense organ, it activates specialized neurons called receptors The receptors respond by converting their excitation into a nerve signal –Think of this as the way a bar-code reader converts a series of lines into an electrical signal that a computer can match with a price

1. Energy contains information about the world (Stimulus). 2. Accessory structures modify energy. 3.Receptors transduce energy into a neural response. 4. Sensory nerve transfers the coded energy to the CNS 5. Thalamus processes and Relays the neural response. 6.Cortex receives input And produces sensation and perception. Elements of a Sensory System: Steps to Sensation

Light enters the eye as waves of electromagnetic energy, a small portion of the varying wave ranges that produces light humans can see Electromagnetic Energy- An energy spectrum that includes short waves of gamma rays to long waves of radio transmission, X-rays, radar Our experience of color varies from other species because of the sensitivity of our vision system

Light’s wavelength (the distance from one wave peak to the next) determines its hue (the color we experience) Includes: red, orange, yellow, green, blue, indigo and violet (ROY G BIV) The eye can detect 7 million separate hues Amplitude- The brightness of light as determined by height of the wave The taller the wave, the brighter the color

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The clear bulge on the front of the eyeball Begins to focus the light by bending it toward a central focal point Protects the eye

The adjustable opening in the center of the eye that controls the amount of light entering the eye (surrounded by the iris) In bright conditions the iris expands, making the pupil smaller. In dark conditions the iris contracts, making the pupil larger.

Iris A ring of muscle tissue that forms the colored portion of the eye; creates a hole in the center of the iris (pupil) Regulates the size of the pupil by changing its size-- allowing more or less light to enter the eye

A transparent structure behind the pupil; focuses the image on the back of the eye (retina) Muscles that change the thickness of the lens change how the light is bent thereby focusing the image Glasses or contacts correct problems in the lens’ ability to focus

14 Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects (eyeball focuses images in front of the retina) Farsightedness: A condition in which faraway objects are seen more clearly than near objects (eyeball focuses images behind the retina)

Light-sensitive surface with cells that convert light energy to nerve impulses to process visual information At the back of the eyeball Made up of three layers of cells –Receptor cells –Bipolar cells –Ganglion cells

17 Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which are for the optic nerve

18 Action Potentials Retinal ganglion cells and thalamic neurons break down visual stimuli into small components and have receptive fields with center-surround organization ON-center OFF-Surround

© Prentice Hall, 1999 Anatomical Pathway in the Retina

These cells are present in every sensory system to change (transduce) some other form of energy into neural impulses In sight they change light into neural impulses the brain can understand Visual system has two types of receptor cells – rods and cones

Visual receptor cells located in the retina Can only detect black, white, and gray Necessary for peripheral and twilight vision, when cones don’t respond

Visual receptor cells located in the retina Can detect sharp images and color Need more light, usually daylight Many cones are clustered in the fovea Marker demonstration

The central focal point of the retina The spot where vision is best (most detailed)

The nerve that carries visual information from the eye to the occipital lobes of the brain

27 Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex

The point at which the optic nerve travels through the retina to exit the eye There are no rods and cones at this point, so there is a small blind spot in vision

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A blind spot exists where the optic nerve exits through the retina, because there are no rods or cones at this point. To find your blind spot, close your right eye and look at the cookie monster. Maintain your focus on the cookie monster and slowly adjust the distance of the screen from your eyes until the cookie disappears. Under normal circumstances, you are unaware of your blind spot because one eye sees what the other does not.

Close both of your eyes. Press gently in the corner of one eye. You should “see” a pattern caused by pressure of your finger, not by light These light sensations are phosphenes, or visual images caused by fooling your visual system into thinking it sees light

FYI- What is Red Eye? What is red eye, that annoying red dot that appears in people’s eyes in pictures, and why does it occur? Usually, red eye occurs in pictures where the surrounding illumination is dim, so the flash from the camera must be used to take an accurate picture The flash is so quick that the iris doesn’t have time to contract, making the pupil big enough to see right through to the red retina! Cameras with so-called “red eye detection” features provide a series of quick flashes that warn the eye that a picture is about to be taken The iris reacts to the light and shrinks the pupil down so the retina is protected from the bright flash

35 Feature Detection: Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement Shape Detection: Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses

36 Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, and movement etc Our perceptions are a combination of sensory (bottom- up) and cognitive (top-down) processes

37 From Sensation to Recognition