SENSATION AND PERCEPTION PART 1B

Sensation & PerceptionPART I : Sensation & PerceptionPART I AP PSYCHOLOGY

Fovea : Fovea Small are of the retina in the most direct line of sight Where cones are most concentrated for highest visual acuity in bright light

Dark and Light Adaptation : Dark and Light Adaptation Dark Adaptation Adjusting to the darkness Camping theater Light Adaptation Eyes become less sensitive to light in high illumination Why does this occur? Chemical changes in rods and cones Neural changes in the receptors and in retina

Information processing in the retina : Information processing in the retina Light strikes rods and cones Creates neural signals Signals sent along optic nerve Axons exit optic nerve through the optic disk Information sent to the brain

Before the information is sent to the brain : Before the information is sent to the brain Processing goes on in the retina before the info goes to the brain 100 million rods and cones combine and travel along 1 million axons in the optic nerve Receptive field- retinal area that affects the firing of that cell Lateral Antagonism- occurs when neural activity in a cell opposes activity in surrounding cells

Vision and the Brain : Vision and the Brain Light falls on the eye but you see with your brain How does visual information get to the brain? Axons Optic Chiasm Two Pathways Thalamus (way station of the brain) Magnocellular channel Parvocellular Channel Superior Colliculus (in midbrain) Parallel Processing Simultaneously extracting different kinds of info from the same input

Visual Information Processing : Visual Information Processing Parallel Processing simultaneous processing of several aspects of a problem simultaneously

Processing Visual Information : Processing Visual Information Ganglion cells— neurons that connect to the bipolar cells, their axons form the optic nerve Bipolar cells— neurons that connect rods and cones to the ganglion cells Optic chiasm— point in the brain where the optic nerves from each eye meet and partly crossover to opposite sides of the brain

Information Processing in the Visual Cortex : Information Processing in the Visual Cortex Primary Visual Cortex- occipital lobe Hubel and Wiesel Research done with cats Nobel Prize Identified special types of cells in PVC Simple clues Complex cells Why is this research important? Specializations Feature detectors

Color Vision : Color Vision Lights are mixtures of various wavelengths Longest wavelengths= red Shortest wavelengths= violet Three Parts of Light Wavelength- hue Amplitude- brightness Purity- saturation 2 kinds of color mixtures Subtractive- removal of some wavelengths of light Additive- color mixing by superimposing light

Color Mixing : Color Mixing Two basic types of color mixing subtractive color mixture example: combining different color paints additive color mixture example: combining different color lights

Subtractive Color Mixture : Subtractive Color Mixture +

Additive Color Mixture : Additive Color Mixture By combining lights of different wavelengths we can create the perception of new colors Examples: red + green = yellow red + blue = purple

Color Blindness : Color Blindness Most people with color-deficient vision are not color blind. Dichromate Not completely color blind Make due with only two color channels Most common dichromate is red-green deficient

Color Blindness : Color Blindness Photo and clips seen by normal person. Photo and clips are seen by a yellow-blue blind person. Photo and clips are seen by a totally color blind person. Photo and clips seen by a red-green blind person.

Slide 16 : Color Vision Some people cannot tell the difference between certain colors. The most common form is the inability to see the colors of red or green.

Color-Deficient Vision : Color-Deficient Vision People who suffer red-green blindness have trouble perceiving the number within the design

Color Vision : Color Vision Our visual system interprets differences in the wavelength of light as color Rods are color blind, but with the cones we can see different colors This difference occurs because we have only one type of rod but three types of cones

Trichromatic Theory of Color Vision : Trichromatic Theory of Color Vision Researchers found that by mixing only three primary lights (usually red, green and blue), they could create the perceptual experience of all possible colors This led Young and Helmholtz to propose that we have three different types of photoreceptors, each most sensitive to a different range of wavelengths

Visual Information Processing : Visual Information Processing Trichromatic (three color) Theory of Color Vision Young and Helmholtz three different retinal color receptors red green blue

Opponent Process Theory of Color Vision : Opponent Process Theory of Color Vision Edward Hering Some aspects of our color perception are difficult to explain by the trichromatic theory alone Example: afterimages if we view colored stimuli for an extended period of time, we will see an afterimage in a complementary color

Opponent Process- Afterimage Effect : Opponent Process- Afterimage Effect

ComplementaryAfterimages : ComplementaryAfterimages

Slide 24 :

Opponent-Process Theory : Opponent-Process Theory To account for phenomena like complementary afterimages, Herring proposed that we have two types of color opponent cells red-green opponent cells blue-yellow opponent cells Black-white opponent cells

Which theory is correct? : Which theory is correct? Our current view of color vision is that it is based on both the trichromatic and opponent process theory George Wald-Nobel Prize Winner 3 types of cones Each sensitive to a different band of wavelengths (colors) Supports the trichromatic theory Other Research Cells in retina and visual cortex respond positively to red versus green and blue versus yellow Ganglion cells in retina are excited by green and inhibited by red Supports the opponent processing theory

Overview of Visual System : Overview of Visual System The eye is like a camera, but instead of using film to catch the light we have rods and cones Cones allow us to see fine spatial detail and color, but cannot function well in dim light Rods enable us to see in dim light, but at the loss of color and fine spatial detail Our color vision is based on the presence of 3 types of cones, each maximally sensitive to a different range of wavelengths

Perceiving Forms, Patterns, and Objects : Perceiving Forms, Patterns, and Objects

REVERSIBLE FIGURES : REVERSIBLE FIGURES Drawing compatible with two interpretations that can shift back and forth Based on your perception, you will see one or the other

Jazz lady : Jazz lady

Donkey or Seal? : Donkey or Seal?

Duck or Rabbit? : Duck or Rabbit?

Face or Dragon? : Face or Dragon?

Young Woman or Old Lady? : Young Woman or Old Lady?

Old Man, Old Lady, Young Lady : Old Man, Old Lady, Young Lady

Angel bats : Angel bats

How do you perceive forms? : How do you perceive forms? Subjectively More than receiving signals (sensory input) Involves the interpretation of those signals (sensory input) Not just as simple as S-R psychology

Our Interpretation of Stimuli : Our Interpretation of Stimuli Expectation Provided Information or Cues Perceptual Set Readiness to perceive a stimulus in a particular way Organization Feature Analysis

Perceptual Set: A readiness to perceive a stimulus in a particular way : Perceptual Set: A readiness to perceive a stimulus in a particular way Selection What you focus your attention on can effect your perceptual set Inattentional Blindness (AKA-change blindness) Failure to see fully visible objects or events in a visual display

Inattentional Blindness : Inattentional Blindness

Feature Analysis: Assembling Forms : Feature Analysis: Assembling Forms Process of detecting specific elements in visual input and assembling them into a more complex form. Bottom-Up Processing Top-Down Processing Subjective contours

Bottom-Up Processing : Bottom-Up Processing Analysis that begins with the sense receptors and works up to the brain’s integration of sensory information Progresses from individual elements to whole elements. Detect specific features of stimulus Combine specific features into more complex forms Recognize Stimulus

Top-Down Processing : Top-Down Processing Information processing guided by higher-level mental processes Progresses from the whole to the individual parts Formulate perceptual hypothesis about the nature of the stimulus as a whole Select and examine features to check hypothesis Recognize stimulus As when we construct perceptions drawing on our experience and expectations

Subjective Contours : Subjective Contours Top-Down Processing You perceive contours (boundaries) where none exist

Looking at the whole picture: Gestalt Principles : Looking at the whole picture: Gestalt Principles “the whole can be greater than the sum of its parts” Top-Down Processing at work in Gestalt Psychology EX: Phi Phenomenon The illusion of movement created by presenting visual stimuli in rapid succession Picture book Motion pictures

Motion Perception : Motion Perception Phi Phenomenon an illusion of movement created when two or more adjacent lights blink on and off in succession. (Christmas lights)

Figure and Ground: Organization in the visual system (top-down) : Figure and Ground: Organization in the visual system (top-down) People organize visual perceptions by dividing visual displays into what is there (figure) and the backdrop (ground) Figure More presence Seem closer Ground Appear farther away Less prominent

Perceptual Organization : Perceptual Organization Figure and Ground--organization of the visual field into objects (figures) that stand out from their surroundings (ground)

Goblet or Faces? : Goblet or Faces?