Sensation All sensory systems operate the same, they only use different mechanisms 1. Have a physical stimulus (e.g., light) 2. The stimulus emits some sort of energy 3. Energy activates some sort of receptor system What is Sensation, Perception, and Cognition 1
Sensation The receptor system is designed to convert (transduce) the energy to action potentials. You then organize the physical energy to neural energy by electrical/chemical reactions. Perception You then organize and filter the energy as the information progresses through different neural systems. Ultimately, you develop patterns and process the material 2
Cognition Allows you to determine what the pattern means. So Sensation is involved with detecting the stimulus and converting the information to action potentials. Perception is involved with organizing the action potentials. Cognition is involved with giving the organization some meaning that we can understand. Vision 3
Light Consists of energy particles called photons Characteristics of a light wave. Are examined by machines that measure them in sine waves. 1. The number of photons Determines the intensity of the light Shown by the height of a sine wave 2. The distance between the peaks of the sine wave Called the wavelength 4
Electromagnetic Spectrum. There are a variety of wavelengths. Ultimately, all the waves make up the electromagnetic spectrum. Called electromagnetic because photons have both electrical and magnetic properties. Low wavelengths - Gamma and x rays High wavelengths - AM and FM radio Visible light occupies a narrow band of the electromagnetic spectrum between 400 750 nanometers (1 billionth of a meter) Longer wavelengths are red in color Shorter wavelengths are blue/violet in color White light consists of all wavelengths. 5
The Eye Has a variety of structures Sclera Is a tough white coat Encloses the eye except at the front where it bulges out to form the cornea Cornea Is a thin, clear, outer cap Does most of the focusing of the eye (75%) Is where light first enters the eye. Heals very rapidly (usually 24 hours) Can be altered for myopia to give normal vision 6
Iris Is a muscle and colored part of the eye Is circular and shaped like a donut Expands and contracts the hole in the middle Pupil Is the hole in the middle of the Iris Allows light to enter the eye Lens Light passes through the pupil and through the lens Lens helps to focus light on the retina Is involved with finer focus than the cornea Has muscles that make it flatter or more rounded 7
Retina Is where light finally falls. Is what does the seeing Is part of the brain that has moved during the evolutionary process into the eye Has several structures and types of neurons located in the back of they eye. 8
Sensory receptors Are located in the back of the eye Called Rods and Cones Rods Look like tall towers Are located toward the periphery of the eye Approximately 120 million Don t see color Operate well in the dark Are not good at fine distinctions Are very good at motion detection (Deer and Elk) 9
Cones Are smaller than rods Are located in the middle of the eye in a structure called the Fovea There are approximately 6-8 million cones Need a lot of light to work See color Are very good at fine distinctions Are poor at motion detection 10
Three Types of Cones Each is sensitive to a different wavelength Red = 650-700 Nanometers Green = 500-550 Nanometers Blue = 400 Nanometers 11
Purkinje Shift Because of the amount of light, Rods and Cones work together at dusk. Result - Blues and greens appear deeper. Dark Adaptation Occurs after about 20-30 minutes of dim light Rods are fully activated to see in the dark Cones are not working 12
Ultimately Receptors synapse to other neurons called Bipolar cells Bipolar cells then connect to other neurons called Ganglion cells However, both Bipolar and Ganglion cells receive information from other neurons in the eye called Amacrine and Horizontal cells Result The first level of organization for vision occurs in the eye. 13
Axons from ganglion cells combine and leave the eye from a structure called the Blind Spot. No receptors are located in the blind spot Optic Nerve The axons form a nerve called the Optic Nerve 75% of all fibers from the Optic Nerve cross to the opposite side of the brain at a structure called the Optic Chiasm 14
Fibers then go to the Lateral Geniculate Nuclues which is part of the Thalamus for more organizational processing and the Superior Colliculus to coordinate tracking movement 15
Ultimately all Fibers from the eye end up in area 17, 18, and 19 of the Occipital lobe. Two Theories of Color Vision Trichromatic Theory (Young & Helmholtz) Holds the eye has three types of cones sensitive to different wavelengths: Red, Green, Blue People see different colors because the eye does its own color mixing. Light of any color can be made by combinations of these three wavelengths. 16
Opponent Process Was discovered because Yellow appears to be a primary color too. Contends that people visualize color as opponent pairs Red Green Blue Yellow Black White Explains the concepts of afterimages Also explains why we are color blind to particular types. Ultimately, both theories work together to explain color vision better than individually. 17