Perception Flashcards
What are the 5 steps in perception?
stimulus, transduction, sensation, perception, recognition
What are the different types of stimulus?
Distal stimulus: the source of the change in your organism e.g. the light.
Proximal stimulus: changes in retina for example. The change occurs directly in the body.
What is sensory modality and give examples?
sensory modality, is one aspect of a stimulus or what is perceived after a stimulus.
For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation.
What are the characteristics of sensory receptors?
Range: each sensory modality responds to a limited range of stimuli.
Adaptation: for the eyes, there is a depletion of chemicals, e.g. (machband effect?). Adjustment of the sensory system’s sensitivity to the current environment (e.g. when it goes dark your eyes adapt).
Acuity: how well we can distinguish among stimuli within a sensory modality. The smallest difference in color you can perceive.
Describe vision as a sensory modality.
Retina: cones for colors. Rods for night vision but not detailed. There is a blind spot in the eye.
Relative encoding: so what matters is contrast. Absolute encoding would limit us in how many colors we can perceive.
Describe auditory and vestibular modalities
Auditory: air vibration and waves of pressure change, vibrations magnified in the cochlea.
Vestibular system: balance and movement.
All sensory information (except olfactory which goes directly to the brain) passes through the thalamus and goes to the different parts of the brain to be further processed.
What is transduction?
Transduction (peripheral processing): transformation of one type of energy e.g. light, into another electric energy in the brain. Ion channels are closed if there is PSP.
What is the difference between sensation and perception?
Sensation: bottom-up activation of our sensory system by a stimulus. Occurs when sensory organs absorb energy from a physical stimulus, the sensory receptors transform into electric signals that go into the brain.
Perception: it reflects the idea that you recognize what you are sensing.
Describe the difference between structuralism and gelstalt.
Structuralism: adding up sensations.
Gestalt: the whole differs from the sum of its parts. Not just the sum of its sensations. It is not just adding single features…
What is the sensation vs perception debate?
Sensation vs perception debate: apparent motion from one rectangle to another but it is really just two rectangles flashing. The blue circles which are moving.
You can manipulate the movement of the red dot (look at the paper). Example of the triangle and cube, also the arrow/lines with the illusion of one being longer than the other. So discrepancy of what the retina senses and what your brain perceives! So perception is an inference. Example with blurry images where the sensation is noisy but if the context is generous then we can perceive. The blob example.
What is the theory of unconciuous inferences?
Perception is the result of unconscious assumptions.
Likelihood principle: we perceive the object that is most likely (past experiences) to have caused the pattern of the stimuli we receive.
When you are a baby, all the sensations are noise, neurons are less activated. But as you grow you get statistical regularities and networks that will be used over and over again as an adult. Example of the rectangles.
Describe perception as a result of bayesian inference/theory.
Perceiving is inferring from the 2D image created in the retina (proximal stimulus) what caused it (distal stimulus) in a 3D environment → inverse problem in the sense of Bayesian statistics using prior belief and posterior and likelihood.
Info sent by proximal stimulus so perception is the best hypothesis to make sense of what you sense.
Posterior beliefs are a combination of evidence and prior beliefs. Depends on the number of parameters for the crossed line example (two intersecting lines or two acute angles, so you have two models to compare). Same example for the image of the duck that also looks like a rabbit at the same time.
Perception is model comparison. Parsimony is key to the model comparison. You want a representation of the world where you can make predictions of what will happen in the world.
What is perceptual constancy?
Perceptual constancy: tendency to see objects as having standard shape, size, color or location regardless of changes in the angle, perspective, distance or lighting (proximal changes). Responsible for the ability to identify objects under various conditions.
Example of perception not equal to sensation
What we perceive is not what we see. Ames’ room. Size and color constancy.
The dress: warm vs cool illumination.
We perceive colors as they should be given the environment, we do not perceive colors that are actually entering the eye.
What is object recognition?
Object recognition: matching what you sense with something you have in memory. Noise with dog example.
What are some diseases that impact object recognition?
Visual agnosias: incapacity to recognize subjects.
Prosopagnosia: incapacity to recognize faces.
Which are the visual pathways in the brain?
Two visual pathways: the what which is in the temporal lobe. The where in the parietal lobe. Fusiform face area for face recognition.
What is the direct approach of object recognition?
Direct approach: sense of objects comes from their affordance (possible uses, what they are built for). No mental representations needed. Stimuli carry enough information to be correctly perceived and identified. Importance of bottom-up approach. The basic process of object perception and recognition is a process of resonance (receiver analogy)
What is size constancy?
Size constancy refers to the fact that our peceptions of the size of objects are relatively constant despite the fact that the size of objects on the retina vary greatly with distance
Assuming size constancy, our visual system estimates the size of any object as follows : retinal distance size multiplied by the assumed distance. Monster example: we think one monster is bigger than the other based on contextual cues such as perpective, but actually they are the same size
What is color constancy?
Color constancy refers to our ability to perceive colors as relatively constant over varying illuminations (i.e. light sources). For example, a red apple will still look red on a sunny day or cloudy day – or in a grocery store or a home.
What is the indirect approach in object recognition?
Importance of top-down processes:we perceive and interpret the stimuli in the light of our beliefs, knowledge or expectations
* 4 postulates on object recognition process
–Active process(not only stimuli driven)
–Does not directly come from stimulus(hypothesis driven)
–Influenced by motivation
–Our desires or beliefs can lead to illusions
What is perception based on according to Gestalt?
Principle of proximity : proximal elements in the visual field tend to be grouped
Principle of similarity : similar elements tend to be perceived together
Principle of continuity: we are grouping the elements that need less changed or interruption
Principle of closure: we fill the empty elements
What is representational momentum?
Representational momentum is a small, but reliable, error in our visual perception of moving objects. Instead of knowing the exact location of a moving object, viewers actually think it is a bit further along its trajectory as time goes forward.
For example, people viewing an object moving from left to right that suddenly disappears will report they saw it a bit further to the right than where it actually vanished.
The perceived offset point is always shifted from the true location in the direction of movement → Anticipated motion
What is object recognition by template matching?
It is a theory that assumes every perceived object is stored as a “template” into long-term memory.[4] Incoming information is compared to these templates to find an exact match. In other words, all sensory input is compared to multiple representations of an object to form one single conceptual understanding.
The theory defines perception as a fundamentally recognition-based process. It assumes that everything we see, we understand only through past exposure, which then informs our future perception of the external world.For example, A, A, and A are all recognized as the letter A, but not B.
