L07 - Sensations and Perceptions Flashcards
Who is Gustav Fechner?
He was interested in vision. Vision comes from psychophysics (the science of defining quantitative relationships between physical and physiological events). He was blind for staring at the sun too ling - eventualy got his vision back. He started the study of sensations and perceptions.
What is absolute threshold?
The level of stimulus intensity required to create a conscious experience
What is the signal detection theory?
Accounts for individual biases. This changes between people but it is the difference between people’s visions.
What is sensation?
The ability to detect a stimulus. Features of an environment that are used to create an understanding of the world.
What is perception?
The act of giving meaning to a detected stimulus. Combining of sensations arriving from the sensory system with prior knowledge.
What is transduction?
Conversion of one energy to another. Process where stimuli (i.e,) light (soundwaves maybe) are converted to neural electrochemical energy (action potential).
Perception; How do we assign meaning to income sensory information?
Bottom-up processing!
What is the difference between bottom-up processing and top-down processing?
Bottom-up processing states that it is a day to driven species - look for info, once we know, then we figure out what we see/hear… *Very unbiased approach
Ex. We recognize that the lines /-\ make A
Top-down processing is the idea that we have memory in mind - like a template - that we use as sensory information and we look to fill in this template. *Biased approach
Ex. There are a bunch of lines and dots and if I tell you that it is a dog, you will start to see the dog and believe it is a dog.
What is the Extromission theory of vision?
“Vision comes from eyes sending out beams”
The opposite of the Intromission theory.
First suggested in 4th century B.C. Plato - stating that the eyes send out vision beams which seize objects. 50% of Americans today still believe in the extromission theory.
What is the Intromission theory of vision?
“Vision comes from objects entering the eyes”
The visual perception of objects comes from some representation of the object entering the eyes.
How does light reflect in our eyes according to the Intromission theory of vision?
Sun emits photons
Photons emit light
Comes to Earth
Scattered around at the atmosphere
Ones that make it through bounces off objects or are absorbed
Light reflects in our eyes
Explain Light.
Light is an electromagnetic energy that exists both as particles (photons) and as waves. We can only detect a small band. (400-700nm)
Terms to know regarding light
Wavelength - perceived hue (the distance between 2 peaks - hue means colour)
Frequency - cycle rates
Amplitude - perceived intensity (increase of height in peaks)
What are Rods?
Photoreceptors
Dim light (“night vision”)
Sensitive to all wavelengths of light
Black and white vision
What are Cones?
Photoreceptors
Bright light (“daylight vision”)
Sensitive to blue/red/green wavelengths of light
“Color vision”
What do photoreceptors do?
Transduce* light into neural activity
Found in the back of the retina
Two types of photoreceptors (rods and cones (few cones – 5mill and lots of rods – 100mill))
Tetrachromats
Humming birds are tetrachromats
Can see UV wavelength
What is the blindspot?
The point where the optic nerve leaves the eye
The nerve is in the way so there cannot be any photoreceptors
The visual system usually fills in blindspot information from the surrounding area
What are Bipolar Cells?
Intermediate cells that determine the information flow from photoreceptors to ganglion cells
There are two types of bipolar cells
Diffuse bipolar cells
Midget bipolar cells
What are diffuse bipolar cells?
Found in the periphery
Respond to around 50 rods – increase sensitivity but reduced activity
Convergence of information – many RODS = one diffuse bipolar cell
What are midget bipolar cells? Hint - Cones
Found in the fovea (center)
Receive input from a single cone and pass on info to a single ganglion (1 midget bipolar, 1 CONE)
Where are ganglion cells located?
In the retinal ganglia - the final layer of the retina
contains m-cells and p-cells
What are m-cells? Hint; in the retinal ganglia
Large ganglion cells
Mostly respond to RODS cells via diffuse bipolar cells
What are p-cells? Hint; in the retinal ganglia
Small ganglion cells
Mostly respond to CONES via midget bipolar cells