Lecture 2: Sensation & Perception Flashcards
Which key themes are a concern in the study of sensation and perception?
- Bottom-up vs. Top-down
- Serial vs. Parallel Processing
- Conscious vs. Unconscious
- Processing
- Attention
What is the experience error?
- assumption that the structure of the world is directly given from the light that the eye receives
What is the inverse projection problem?
- fundamentally ambiguous mapping between sources of retinal stimulation and the retinal images that are caused by those sources
- i.e. Light from an object is inverted as it falls on the retina. The same pattern of light could be caused by an infinite number of different objects, yet our brains usually manage to make the correct interpretation.
What are fixation-saccades cycles?
- Our eyes don’t take in a while picture but have one pieced together from the different things we focus on.
- Vision is suppressed during a saccade so our visual experience is stitched together from fixations
What is a saccade?
- fast movement of an eye
When does change blindness occur?
- occurs if a change in a visual scene occurs during a saccade
What is agnosia?
- deficit in recognition despite normal vision
What is apperceptive agnosia?
- inability to name, match, or discriminate visually presented objects
- patients can’t combine basic visual information into a complete percept
- show deficits in copying
What is associative agnosia?
- inability to associate a visual pattern with meaning i.e. they can’t recognize what they see
- patients are able to combine visual features into a whole
- ability to copy pictures but unable to name them
What separate steps in visual processing can be inferred from patients with agnosia?
- Input/Sensation
- Basic visual components assembled
- Meaning is linked to visual input
What is the basic path that light takes in entering the eye?
- enters through the pupil
- focused by the lens (and cornea)
- projected onto the retina
What is the responsibility of photoreceptors in the retina?
- receiving light energy
- changing it into a signal the brain can understand
What is the ratio of rod to cone distribution in the eye?
2:1 with rods to cones
Where does the light information go once it is processed by the photoreceptors?
- Photoreceptors send information about light to the bipolar cells, which send that information to ganglion cells
- Each time the signal is passed to another type of cell, it converges
- Great deal of compression so when signals reach cortex they are already summarized and processed
What is the general process for visual processing?
- Information reaches cortex for visual processing
- Information is sent to iconic memory
Visual attention selects items
Information is sent for further processing and to memory
What is the first step of visual processing and what happens?
- Information reaches cortex for visual processing
- The cortex receives a pattern of light pixels from the retina
- The primary visual cortex (V1) combines those pixels to create lines and edges
What is the second step of visual processing and what happens?
- Information is sent to iconic memory
- Iconic memory accounts for visual persistence
- Explains why we perceive a continuous visual image despite fixation-saccade cycles
- We are not aware of everything in iconic memory
What is iconic memory?
- A limited capacity store that holds basic visual information for a very limited amount of time
Describe Sperling’s Sensory Store investigation.
- Sperling wanted to know how much information is available after a very brief presentation
- When asked to remember as many letters as they can (whole report), people can only remember 3-4 items
- When cued to report one row only (partial report) based on a high, mid, or low tone, people could remember approximately 3 items in that row (76%)
What did Sperling conclude in his investigations into iconic memory?
- By varying the time delay between the offset of the display and onset of the tone, Sperling discovered information in iconic memory decays very rapidly
> duration is ~150ms - Sperling reasoned that people had access to approximately 9 items in iconic memory at any given time (including size, shape, colour, etc.)
What is the third step of visual processing and what happens?
- Visual attention selects items
- Attention selects some information from iconic memory for cognitive processing
- Focal attention can select 3-4 items at a time and move it to short-term memory
What is the fourth step of visual processing and what happens?
- Information is sent for further processing
- The visual system detects patterns of contours and edges
- According to template theory, we have a mental ‘stencil’ for an array of different patterns
- We have a system for analyzing each distinct feature of a visual item
What is the Pandemonium model?
- mental demons shout as they attempt to identify patterns
- pattern encoded by data demons
- computational demons have a single, simple feature it is trying to match in the stimulus pattern
> when it matches it shouts loudly - cognitive demons listen for features and shout if they think they hear some/all of their features
- loudest cognitive demon is heard by the decision demon, who has the final say in recognizing and categorizing the pattern
What is the physiological support for feature matching theory?
- feature detector neurons in primary visual cortex
What is recognition by components theory?
- 3D objects are recognized by parsing them into geons (tubes, pyramids, etc.)
- Geons are view-point invariant because they have nonaccidental properties
- We pay attention to edges and vertices to notice which maintain their relationship regardless of viewing angle
What is one criticism of recognition by components theory?
- Even without vertices occluded, we have trouble recognizing objects from non-canonical viewpoints
What are the arguments against bottom-up processing?
- Analyzing each feature one at a time takes a LONG time
- Not all objects can be broken into distinct features
- Pattern recognition can depend on top-down/conceptually driven effects
What are some examples of conceptually driven effects of visual processing?
- use what we know and expect of the world to perceive
- illusion where we see shapes with dark gradients as concave or convex because we expect light to hit the top
What is gestalt psychology?
- concerned with how perception gets organized into meaningful units
- identify characteristics of perception which help determine which components of a stimulus group together
What are the Gestalt principles?
- Law of proximity
- Law of similarity
- Law of good continuation
- Law of closure
- Law of common region
What did Tanaka & Farah discover about face processing vs. object processing?
- it is a lot easier to recognize parts of house than parts of faces
- facial processing is configural
What did Thompson discover about facial processing?
- face inversion effect
- people don’t notice the face is inverted because we process the whole face and feature relationships i.e. facial processing is configural
- if we were analytically processing it we would notice the inverted features
What did Cooper & Wojan discover about facial processing?
- moved either one eye or two and asked to identify famous people
- people recognized the two-eyed distortion less
- suggest face identification is based on a holistic, coordinate-based representation of the stimulus face
What are the three layers of the retina?
- rods and cones
- bipolar cells
- ganglion cells
What are rods and cones?
- neurons stimulated by light
- begin the process of vision
What are bipolar cells?
- collectors of the patterns of firing in rods and cones
- shuttle to the ganglion cells
What is the optic nerve made of?
- bundles of the axons of ganglion cells
What is a more accurate description of how the eyes transmit information to the brain?
- each eye transmits to both hemispheres
- however visual fields are projected contralaterally
What is the convergence of rods and cones?
RODS: high convergence i.e. several rods to one ganglion cell
CONS: little convergence i.e. 1-3 cones to one ganglion cell, gives more detail in visual field
What is the fovea?
- concentrated area of cones
- provides most accurate and precise vision
What is sensation?
- reception of stimulation from the environment and encoding of it into the nervous system
What is perception?
- process of interpreting and understanding sensory information
What is backward masking?
- later visual stimulus interferes with memory for the prior stimulus at the same location
What did Loftus & Irwin show about eye fixation?
- temporal integration (perceiving two separate events as if they had occurred at the same time) happens seamlessly if there isn’t a large amount of delay
What is trans-saccadic memory?
- memory used across a series of eye movements
- stitches fixations into smooth movement
- uses object files
> iconic representations of individual objects used to track what is going on in the world
What is the figure-ground principle?
- people assign the subject of their attention as the figure or foreground and relegate everything else to the background
Describe the template approach.
- we categorize visual data in templates, stored models of all categorizable patterns
- flawed in that we can’t possibly categorize every single thing in the world
What are three important ideas in the Pandemonium model?
- feature detection model
- parallel processing (demons work at the same time)
- problem-solving process (features must be put together but sometimes it’s not always done correctly)
What was the experiment Hubel and Weisel performed concerning V1 and what were the results?
- using electrode implant procedures, they found neurons in cats’ brains that responded only to vertical lines, or horizontal lines
- suggests feature detection has physiological status in nervous system
What is beta movement?
- illusory perception of things in motion i.e. like frames in a movie
What is phi movement?
- illusory perception of flowing movement i.e. Christmas lights lighting in succession
