Sensation & Perception To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. The process by which sensory systems and the nervous system receive stimuli from the environment is sensation. When we select, organize, and interpret our sensations, the process is called perception.
Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”
Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT
Making Sense of Complexity Our sensory and perceptual processes work together to help us sort out complex images. “The Forest Has Eyes,” Bev Doolittle
Can you read this? Ancordicg to a reaesrch at CarbmidgeUniveristy, it dosen'tmaettr in wahtodrer the letters in a wrod are. The olnyimprotanttihng is taht the fsrit and lsatlteter be in the rihgtpcale. The rset can be a toatlmses and you can slitlraed it wiuhottproelbm. Tihs is becuase the huamnmniddeos not raedeevry letter by iestlf, but the wrod as a whloe.
Exploring the Senses What stimuli cross our threshold for conscious awareness? Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time.
Absolute Thresholds VISION: Candle Flame seen at _________ on a clear night HEARING: Tick of a watch under quiet conditions at________ TOUCH: A bee’s wing falling on your cheek from __________above 30 miles 20 feet One centimeter
Absolute Thresholds SMELL: __________ of perfume diffused into a three-room apartment TASTE: __________ of sugar in two gallons of water 1 drop 1 teaspoon
Psychophysics A study of the relationship between physical characteristics of stimuli and our psychological experience with them. How we detect events in our environment using our sensory systems
Subliminal Threshold Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness. Kurt Scholz/ Superstock
Weber’s Law Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Minimum amount needed to notice difference Quarters/Envelope/Shoes Activity
The Point? • Difference thresholds grow with the magnitude of the stimulus
Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Put a band aid on your arm and after awhile you don’t sense it.
Marker Activity Sniff a marker and rate your perception of the intensity of the aroma from 1 to 20. Sniff the marker six times. Each time rate your perception of the intensity of the aroma. This is sensory adaptation! Much like getting used to being in a cold pool of water.
The Stimulus Input: Light Energy Visible Spectrum Both Photos: Thomas Eisner
Wavelength (Hue) Hue (color)is the dimension of color determined by the wavelength of the light. Wavelengthisthe distance from the peak of one wave to the peak of the next.
Wavelength (Hue) Violet Green Orange Red Indigo Blue Yellow 400 nm 700 nm Long wavelengths Short wavelengths Different wavelengths of light result in different colors.
Intensity (Brightness) Intensity:Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.
Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.”
Parts of the eye • Cornea: Transparent tissue where light enters the eye. • Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light. (colored portion of our eye) • Lens: Focuses the light rays on the retina. (creates nearsightedness or farsightedness) • Retina: Contains sensory receptors that process visual information and sends it to the brain.
The Lens Lens:Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.
Retina Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information.
Optic Nerve, Blind Spot & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. Fovea: Central point in the retina around which the eye’s cones cluster. http://www.bergen.org
Test your Blind Spot Blind spot testers: Close your right eye Use your left eye to look at the face on the right side of the paper You should be able to see the face on your left with your peripheral vision Now SLOWLY move the paper away from and towards your face while focusing on the face on the right At some point, the left face will disappear. That is your blind spot!
Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Bipolar & Ganglion Cells Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which converge to form the optic nerve.
Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.
Shape Detection Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. Ishai, Ungerleider, Martin and Haxby/ NIMH
Visual Information Processing 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, movement, etc.
Color Vision Trichromatic theory: Young and von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors.
Try this Activity. You will have about 3 seconds to read the following statement.. tHecoWgAvecOla
thEcoWgAvecOla TheCowGaveCola Want to try again?
Try reading the statement below from right to left. You will have about 3 seconds to read it. Then write it down! “.tar eht was tac ehT”
Did you write “The cat was the rat”? If you did you were incorrect. The correct answer is: “The cat SAW the rat”
Let play it again one more time. You get three seconds to look Very carefully, then write it down! Without Blurting Out!
CONES – Receptors for color vision that work best in the daylight. Located in the Retina which receives focused light. RODS – Receptors for night and side (peripheral) vision. At left, Rods & cones under the microscope
After image experiment. Focus on the center of the circle without moving your eyes for 30 seconds. Then look at the surrounding area. You will see an after image.
Opponent Colors Gaze at the dot in middle of the flag for about 30 seconds. When it disappears, close your eyes and report whether or not you see Britain's flag.
VISUAL DYSFUNCTIONS (cont.) Most common problem; cannot see red or green. Males 8% Females 0.05% Do animals see color? Animals have rods & cones which allow them to see color. This bull must be seeingred!
Color Test One Look at the pictures below. Do you see a puzzle piece in the picture on the left? If you do, you have normal color vision. The picture on the right will give you an idea of how the color picture would look to someone that is totally colorblind. It is the same picture using shades of grey. Without the colors as a reference the image in the picture disappears. Red Deficient Red Deficient Green Deficient
Color Blindness/Color Deficient Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test