PSYD13 Delkurs 1 - Perception Flashcards
Define sensation
The stimulus detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain
Define perception
Making “sense” of what are sense tell us; it is the active process of organising this stimulus input and giving it meaning
Sensory transduction?
The process whereby the characteristics of a stimulus are converted into nerve impulses
What is psychophysics?
Studies the relationship between the physical characteristics of stimuli and sensory capabilities
What is meant by absolute threshold?
The lowest intensity at which a stimulus can be detected 50% of the time, or in other words, the lowest amount of stimulus that is needed for sensory organs to react/cease to react.
What is the Signal Detection theory?
This is theory act as a framework to understand how internal and external factors influence one sensitivity to stimuli, more in particular ones sensitivity to a signal (something important) vs distraction.
What is a decision criterion, in relation the absolute threshold?
Even though absolute thresholds can be a rough estimate of people sensitivity to sensory stimuli, it is inaccurate. This is because people set their own decision criterion, i.e. = a standard of how certain someone must be that a stimulus is present before they will say they can detect it.
What are the 4 possible outcomes of the Signal Detection theory?
Hit, miss, false alarm and correct rejection
What is the difference threshold? (or the just noticeable difference threshold (JND)
The smallest difference between 2 stimuli that people can perceive 50% of the time
Weber’s Law?
The law states that the difference threshold, or JND, is directly proportional to the magnitude of the stimulus with which the comparison is being made. In simpler terms, this means that the greater the intensity of the stimuli, the bigger the difference has to be
Weber fraction?
The aptitude with which we make discriminations across any given class of stimulus range, for example the weber fraction for kinaesthesis (lifted weights) is 1/50, i.e. you can feel a difference in a weight that weighs 50g and 51g
Sensory adaption?
Refers to the diminishing sensitivity to an unchanging stimulus
Why is sensory adaption beneficial for the brain?
Sensory adaption leads to a decrease in neural activity for said stimulus, which allows for an increase in sensitivity for other, perhaps more important stimuli
What are 2 examples of sensory adaption?
Light adaption and dark adaption
What is the span wavelengths that the human eye is sensitive to?
Wavelengths extending form 700 nanometers (red) down to about 400 nanometers (blue-violet).
What is the lens of the eye?
An elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearly objects
What is the retina?
It is a multilayered light-sensitive tissue at the rear of the fluid-filled eyeball
Explain visual transduction
The visual information enters the eye and is reversed by the lens and cast on the retina, which contains the rod and the cone photoreceptor cells. When the sensory information is cast on the retina, the photoreceptorcells transduct the image into nerve impulses through the photopigments. The rods and cones synapse with bipolar cells -> ganglion cells, who’s axon form the optic nerve -> thalamus -> cortex
Rods?
Photoreceptorcells that are sensitive to light (500x more sensitive to lights than cones) and function best in dim light. Are primarily black-and white brightness receptors.
Cones?
Photoreceptorcells that are sensitive to colour that function best in bright illumination
Optic nerve?
Is made up out of the axons of ganglion cells that send visual information from the eye to the thalamus and cortex
Fovea?
Small area in the centre of the retina that contains no rods but many densely packed cones
Optic disk?
Where the optic nerve exits the eye which has no receptors, which produces a blind spot.
Visual acuity?
Our ability to see fine detail
Photo-pigments
Rods and cones translate light waves into nerve impulses through the action of protein molecules called photo-pigments
Dark adaption
The progressive improvement in brightness sensitivity that occurs over time under conditions of low illumination
Explain how dark adaption works
Photopigments are depleted cause by light - cones recover faster than rods but aren’t as light sensitive which means that they aren’t as well fit to produce vision in the dark - after ca 30-40 mins the rods recover and our vision has adapted to the dark
Why are fight pilots advised to wear red glasses or sit in a room with red light?
Because rods aren’t as sensitive to red wavelength light -> the photopigments molecules aren’t depleted cause by high illumination, which results in the rods remaining in a state of dark adaption
What is Young-Helmholtz trichromatic theory?
Helmholtz theory states that there are 3 types of colour receptor in the retina
What are the issues with the trichromatic theory?
- The theory states that red + green produces yellow, which fails to explain how people who are colourblind and cannot see red and green, can still see yellow 2. Cannot explain the phenomenon of an afterimage (when you look at a flag and see it in reverse when you look away)
What is Hering’s opponent-process theory?
The theory states that each of the three cone types responds to two different wavelengths. Hering meant that there are a white-black, a yellow-blue and a red-green opponent process. In each of these opponent processes, we code vision as a tension between wavelengths
What is the dual-process theory?
The theory combines the trichromatic- and opponent-process theories and states that yes, there are 3 types of cones that are sensitive to different wavelengths (blue, green and red) -> opponent processes occur further along in the visual systems, i.e. in the two types of ganglion cells.
What are feature detectors?
A type of cell in the primary visual cortex that respond to different types of visual information
How do we know that there are feature detectors?
Well, Wiesel and Hubel (who won a nobel price for this) did an experiment where they measured neural activity in a cat while it was looking at a rod that was rotating. What they found was that when the rod was at a certain angle, a certain area in the visual cortex had high activity (compared to other angles).
What is the visual association cortex?
Where features of a visual scene are combined and interpreted in light of our memories and knowledge (i.e. compared to the information in hippocampus)
What is parallell processing?
When sensory (ex. visual information) is simultaneously processed and interpreted in separate but overlapping regions, in order to perceive the “whole picture”
