Chapter 4 - Perception Flashcards
1- Explain sensations (exteroceptive vs. interoceptive).
Exteroceptive sensations
* Any form of sensation that results from stimuli located outside the body detected by sensory organs
-vision: light entering eye
-audition: vibrations in the air entering the ear canal
-touch: pressure, heat and vibrations on skin
-gustation: chemical compounds in the mouth
-olfaction: airborne chemical in nasal passage
Interoceptive sensations
* Sensations from inside our body
-Proprioception: Sense of where our limbs are in space
-Nociception: Sense of pain due to body damage
-Equilibrioception: Sense of balance
* Dancers have increased interoceptive accuracy (Christensen et
al., 2017)
-They could estimate heart rate more accurately than non-dancers
-This was unrelated to fitness levels or counting ability
2- Explain synesthesia.
- A neurological condition in which one sense automatically triggers the
experience of another sense
Grapheme-color synesthesia:
-A person sees colors with certain letters or numbers - Genetic component
- One hypothesis is that it is due to cross wiring (cross-talk) between processing areas in the brain
- Artists are eight times more likely to have synesthesia than nonartists
- The cross-talk between sensory areas in the brain increases the ability to think creatively and in metaphors
3- Sensation vs. perception
Stimulus (light, sound, smell)….
Sensory receptors (eyes, ears, nose) + neural impulses= sensation
Brain (visual, olfactory, auditory areas)= perception
* Perception is when meaning is added to
sensory data
* Perceptions are subjective and can change
* According to how you feel, desirable objects will appear
closer/larger than less desirable objects
* A water bottle appears closer than crackers when thirsty
* Hills look steeper when you are tired
4- Explain the McGurk Effect.
When you hear what you see
* A multisensory illusion such that there is a change in auditory perception from visual perception
* A voice articulating a consonant (/ba/) paired with a face articulating another one (/fa/) leads you to “hear” what you “see”
* This shows us that there is an integration of sensory
information
* This also illustrates the dominance of visual input
5- The visual system: Explain early visual processing (sensation) (eyes and the optic nerve)
- Light waves enter the eye and are projected
onto the retina
* The retina, a thin layer of tissue at the back of the
eye, forms an inverted image
* Later processes turn this image around - Photoreceptors in the retina convert light to
electrical activity
* Rods: low light levels for night vision (high sensitivity, low acuity)
* Rods are mostly outside of the fovea, in the periphery
* Periphery of your visual field is less detailed and less accurate
* Cones: high light levels for detailed color vision (low sensitivity, high acuity)
* Cones are most concentrated in the fovea,
which is a small area on the the central part of the visual field
* Center of your visual field is most detailed - The electrical signal is sent to bipolar cells and then to the ganglion cells
- The signal exits through the optic nerve to the brain
(know the pathways and where they cross)
6- Explain information compression.
- Millions of photoreceptors in each retina converge onto 100 x fewer ganglion cells
à optic nerve à brain - Input from the eyes to the brain is compressed
- You don’t ‘see’ everything that is out there in the world
7- Explain perceptual filling-in.
8- Explain the blind spot.
- Photoreceptors are at the back of the retina
(farther from the ‘world’) - Ganglion cells are at the front of the retina
(closer to the ‘world’) - Ganglion cells make up the optic nerve that take
this signal to the brain and have move past the
photoreceptor layer - At this ‘exit location’, there are no photoreceptors so visual stimuli are not received
But we do not ‘see’ our blindspot!
* This is because of perceptual filling-in
* Later visual processes in the brain provide the missing information by
‘interpolating’ visual information (e.g., colors) from surrounding areas
* This is also because the left and right visual fields can compensate for each other’s blind spot
9- Explain early to late visual processing.
- Thalamus: A way-station between sensory
inputs and the cortex - The optic nerve of each eye transmits information to both hemispheres, leading to the principle of contralateral representation
- Left visual field is perceived via the right hemisphere
- Right visual field is perceived via the left
hemisphere
(see image)
10- Explain late visual processing and the two pathways.
- Primary Visual Cortex (occipital lobe) (primary = first place info goes to) contains specialized regions that process particular visual attributes or features (functional specialization)
* Edges
* Angles
* Color
* Light
* Demonstrates functional specialization
* Features of visual input are processed in
different regions
* Damage leads to conscious vision loss
* Demonstrates we can have perception
without awareness - Visual Association Areas interpret visual information and assigns meaning
AND THEN 2 PATHWAYS to the visual association areas.
* WHAT (ventral) pathway
-Occipital to temporal lobes
-Shape, size, visual details
* WHERE (dorsal) pathway
-Occipital to parietal lobes
-Location, space, movement information
* Neuroimaging studies show separation of what and where pathways
Neuropsychological case of dorsal ‘where’ pathway
Goodale & Milner (1991):
* Ventral damage with intact dorsal stream
=Impaired performance on visual object recognition or matching tasks
* Dorsal damage with intact ventral stream
=Accurate performance on object recognition or matching tasks
=Impaired performance on visual guided action (picking up an object
appropriately)
* Some suggest this may mean that dorsal and ventral pathway represent “perception” and “action”
11- What are lessons we can learn from the visual system?
- Visual stimuli is altered at many stages of the
processing pipeline (e.g., inversion, compression,
within the primary visual cortex) - In the cortex, visual input is broken down, processed
separately and then combined to form a perception of an entity - The reality we perceive is a construction of the brain
12- Explain bottom-up vs. top-down processing.
- Bottom-up processing: the influence of information from the external
environment on perception
-Information from the sensory organs (eyes) to the visual cortex - Top-down processing: the influence of knowledge (expectations, context and
goals) on perception
-Information from final stages of higher areas of the brain (prefrontal cortex
or higher visual processing areas) that is sent back to the visual cortex
13- Explain the Constructivist Theory of Perception and use examples of illusions.
Constructivist Theory of Perception:
* Governed by top-down processes
* We use what we know, and current context to predict how to perceive sensory data
* Perception is influenced by stored knowledge and context
* Mental models
* We make unconscious inferences to interpret and to predict
sensory data
Pain perception is subjective
* Perception of pain is partly determined by expectation
* Rate pain of the shock in Phase 2 in the low and high cue trials
* The shock levels were the same across conditions
* Pain ratings were higher in the high-cue than the low-cue
Using knowledge to perceive: The Ponzo illusion (lines and train tracks): assumptions about depth cues
Using knowledge to perceive: Distance and size (2 monsters): assumptions about depth cues
Knowledge to perceive: The world is lit from above: assumptions about shadow cues
Perception is predicted by knowledge
* We use assumptions about what we expect to see to guide perception
* Knowledge, heuristics and schemas that reflect assumptions about how the world works, affects perception
* The specific illusions we are susceptible to illustrate some of these assumptions
(ex: mouse vs face)
Context affects visual perception
* Changes in visual perception based on the surrounding
information (the context)
-Ames room: assumptions about size constancy
* A functional illusion when expectations guide perception
* These are expectations of ‘observation’
-The letters in context effect:
* The ability to read words in sentences even when the letters in the middle of some of the words are mixed up
* This is because you ‘expect’ to see real words in a sentence
-The color in context effect: assumption of context effects
* The context a color appears in can influence how you see that color.
* Color perception depends on both:
* the wavelengths of light that fall on our retina
* Our past experiences of how objects look under different contexts
of illumination
Other examples: the Munker-White illusion, the wolverine, rotating snakes
14- Explain blindsight.
Damage to the primary visual cortex
Blindsight:
* No conscious awareness (explicit perception) of visual
objects in their damaged visual field
* Able to implicitly respond to questions about objects presented in the damaged visual field
* Suggests that they can perceive something without ‘consciousness’ or awareness (implicit perception)
* There is a processing division between conscious (explicit) and
non-conscious(implicit) perception
Test:
* Over trials, turn a light on or
off in the blinded visual field
* Ask patients to guess if the
light was on or off (forcedchoice responding task)
* Patients performed above
chance on the forced-choice
responding task for lights in
the blinded area
Perception is first processed without conscious awareness in the brain
* Raises the idea that awareness is on a
continuum with respect to perception
* Critiques
-There may be other pathways for visual
information to bypass the PVC
-These cases rely on self report
-Some blindsight cases report a non-visual
feeling that something happened
Blindsight and visual imagery
* Activity of patient with blindsight perceiving faces and houses was reduced when compared to control
participants
* Activity of patient with blindsight when imagining faces and houses
was similar to control participants
* Blindsight leads to deficits in consciously processing incoming visual information but not imagery
15- Describe effects of damage to the where/dorsal pathway.
- The dorsal ‘where’
pathway
-spatial information
-depth perception
-estimating movement
and direction of objects
Akinetopsia
* Visual motion blindness: cannot see motion. Instead, perceives motion as a
series of stationary objects
Optic ataxia
* Inability to reach for objects with the ability to name objects
-Problems reaching for a cup of coffee … can
recognize coffee
-Problems pouring milk … can recognize milk
* There might be action specificity in this
pathway
* Selective damage leads to problems with certain types of movement
