Week 5 - Sensation And Perception Flashcards
What is sensation?
The process by which the sense organs (eg. Eyes, ears, skin etc) gather information about the environment
No 1:1 correspondence between physical and physiological reality
What is perception?
The process by which sensory information is selected, organised and interpreted.
But there isn’t a 1:1 correspondence between physical and psychological reality (sensation and perception).
Describe transduction
(Environmental) energy -> neural impulses
Coded in terms of
- intensity
- quality
Sense receptors “transduce” stimuli into signals
Sensory adaptation
Define psychophysics
Study of how we perceive sensory stimuli based on their physical characteristics
Absolute threshold in psychophysics
Is the lowest level of a stimulus (on its own) that we can detect 50% of the time
- a candle 30km away
- 50 odorant molecules
Fechner’s model demonstrates the absolute threshold
Just noticeable difference in psychophysics
Just noticeable difference is the:
-smallest change in intensity of a stimulus that we can detect
Depends on:
- level of intensity of new stimulus
- level of stimulation already present
Eg. Distinguish a quiet and a loud voice
What is attention?
Mental phenomenon of concentration and it’s shifts in focus
- influences by external and internal events
- limited capacity
What is selective attention?
Allows us to select some inputs for further processing and ignore others.
- reticular activating systems (RAS) and basal forebrain activate regions of cortex (eg frontal cortex).
Bottleneck theory of attention in selective attention
Broadbent (1958) - bottleneck theory of attention
- early filtering mechanism (early selection model)
- limited capacity channel
What does the cocktail party phenomenon suggest about selective attention?
Suggests some information gets through the filter.
Even when we selectively attend to a conversation we are subconsciously monitoring other conversations around us.
(Slightly refutes the bottleneck???)
What’re some errors of attention?
Inattentional blindness: a failure to see something in plain sight
Change blindness: the inability to detect changes in scenes when looking directly at them
What is divided attention?
Attention has a limited capacity.
Divided attention: performing multiple tasks simultaneously.
We really shift attentional resources between tasks. The faster and more efficiently we can make these shifts the better we can “multi-task”.
What is considered one wavelength and wave amplitude?
Wave between two peaks. Amplitude height and it determines intensity.
We can only see a very small part of the light spectrum.
Parts of the eye. (Basic)
Sclera (white part)
Pupil (light comes in)
Iris
What’re the two processes of the eye inside ?
- Focussing light on retina
2. Transfixing the image into nerve signals
Features of photoreceptors
Photoreceptors (Rods and cones) turns light energy into electrical signals
Electrochemical process mediated by photo pigments
- rods use rhodopsin
- light bleaches rhodopsin causing fatigue (leads to “after” images like after you turn away from an illusion you feel like you can still see it)
Describe the photo receptors (rods and cones)
Rods:
- low light
- monochromatic
- peripheral vision
Cones:
- bright light
- colour vision
- central vision (fine detail)
Photoreceptors to ganglion cells
Convergence to rods and cones
Light comes in ->Retinal ganglion cell -> amacrine cells -> bipolar cells ->horizontal cells -> cone receptors -> Rod receptors/ back of the eyeball
Low convergence in come fed circuits
1 Retinal ganglion cell -> 1 bipolar cell ->1 cone
High convergence in Rod fed circuits
Multiple Retinal ganglion call -> multiple bipolar call -> multiple Rod
GET COMFORTABLE WITH THE PRIMARY PROJECTION PATHWAYS OF THE VISUAL SYSTEM
Yay
Describe parts of the visual cortex
Different cortical cells respond best to different stimuli.
Simple cells: light if specific orientation at a particular location
Complex cells: specific orientation but less dependant on location
Feature detectors: lines and edges (simple/complex cells), length of lines, shapes, movement, colour etc.
Diagrammed parts of the occipital lobe.
Separated info colours
V1/Primary part of the visual cortex
V4 for colour
What is colour vision?
Different theories explain different aspects of colour vision: opponent and trichromatic theory.
The two theories have BOTH been shown to be correct.
What is one theory of colour vision?
Trichromatic theory: colour vision is based on our sensitivity to three primary colours
- explains colour blindness
- consistent with three types of cones in eyes
What is the opponent process theory of colour vision?
Colour vision as a function of complementary, opposing colours
- red vs. green
- blue vs. yellow
- black vs. white??
Activated vs. inhibited.
Causes of blindness and percentage worldwide
Cataract 47.8% people worldwide treatable.
Glaucoma 12.3% treatable
Macular degeneration 8.7% not treatable
Diabetic retinopathy 4.8% not treatable
Childhood blindness 3.9% some types are treatable.
Outline colour blindness
3 types
- monochromacy
- dichromacy
- (anomalous) trichromacy
Most usual cause is faulty cone development
-genetics: far more common in males
Can also be produced by physical or chemical damage to the eye, optic nerve, or cortical visual processing areas.
What is one test of colour blindness?
Ishihara test. Letters in coloured pictures.
Motion blindness and visual agnosia
Motion blindness (akinetopsia) - inability to perceive motion (or stick together the incoming images)
Visual agnosia- inability to recognise objects, despite normal ability to describe the shape and colour etc (deficit in what pathway)
Prosopagnosia (face blindness)
Cortical blindness and blindsight
Weiskrantz (1986) - cortically blind people asked to
- identify shapes
- identify location
Individuals often claim they can’t do the task because they can’t see. Yet they perform these tasks at above Chance levels. Suggest there are some other elements of the visual system that allows people to operate.
What is Weber’s Law in psychophysics?
Regardless of the magnitude of two stimuli, the second stimulus must differ from the first by a constant proportion for it to be perceived as different.
The Weber fraction for weight is 1/50 for the average person.
For example: 1 blueberry = 1 gram
Therefore 50 grams of blueberries to 100 grams of blueberries
What is the signal detection theory in psychophysics?
Sensation occurs when we judge whether a stimulus is present or not
Two processes co tribute to signal detection:
- Initial sensory process - sensitivity to the stimulus (signal to noise ratio)
- Decision process - the individuals readiness to report detecting a stimulus when uncertain (response bias)
Brightness and hue
We perceive brightness (intensity) and hue (colour)
- mixing lights produces white (additive)
- mixing pigments produces black (subtractive)
What do the lens inside the eye do?
Transparent disk that focuses light rays for near or distant vision
What does the cornea inside the eye do?
Curved, transparent dome that bends incoming light
What does the iris do?
Coloured area containing muscles that control the pupil
What is the pupil?
Opening in the centre of the iris that lets in light
What’s the eye muscle
One of six surrounding muscles that rotate the eye in all directions
What does the retina do
Innermost layer of the eye, where incoming light is converted into nerve impulses
What is the optic nerve in the eye?
Transmits impulses from the retina to the rest of the brain
What is the fovea at the back of the eye? (Point of central focus)
The part of the retina where light rays are most sharply focused
What is myopia and hyperopia?
Nearsighted and farsighted eyes. Nearsightedness or farsightedness results when light is focussed in front of or behind the rear of the eye, respectively.
