Perception Flashcards
Sensation ≠ Perception
Sensation and perception are not the same.
While sensation is input about the physical world obtained by our sensory receptors, perception is the process by which the brain selects, organises, and interprets these sensations. Therefore, sensory processing (the brain) alters perception (= our awareness of our environment).
Is perception a product of processing sensory information
Yes, it is a product of the processing of sensory information. Perception is what we are aware of. Therefore, once the sensory information is in our cortex, we become aware of the sensation.
Explain both bottom-up and top-down processing.
Bottom-up processing refers to the fact that perceptions are built from sensory input.
Scenario: Reading a Street Sign
- Example: Imagine you’re driving in an unfamiliar city and you come across a street sign.
- Perception: You first perceive the individual elements of the sign—shapes, colors, and letters. This is bottom-up processing, as you are starting with the raw sensory input.
- Recognition: Your brain processes these elements to form recognizable letters and words.
- Understanding: Finally, you understand the sign’s message, such as “Stop” or “Main Street.”
- Explanation: In this scenario, you are using bottom-up processing because you begin with the sensory input (seeing the sign) and build up to the recognition and understanding of the sign’s message.
On the Top-down processing how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts.
* Scenario: Listening to a Conversation in a Noisy Room
* Example: You are at a crowded party and trying to listen to your friend’s story.
* Expectations and Knowledge: You use your knowledge of the context (a party setting) and your expectations about the conversation (topics you often discuss with this friend).
* Focus and Interpretation: Despite the noise, you can focus on your friend’s voice and fill in the gaps of any missed words or sounds based on the context and your prior knowledge.
* Comprehension: You understand the story even if some parts were inaudible due to the surrounding noise.
* Explanation: In this scenario, you are using top-down processing because you rely on your prior knowledge, context, and expectations to interpret and understand the conversation despite incomplete sensory information.
What experimental techniques can be used to measure perception?
Simply stating what we observe and comparing that with others.
This was done in the lecture with the dress and strawberry example. Our brain’s interpretation influences our perception of the same visual stimulus. Your brain has a lot of influence over how we perceive the information going in: this is evident in the fact that it can ‘correct’ what you’re seeing.
Our approach: if we can determine how perception changes under various conditions, then we should be able to predict these changes and therefore understand perception
- Threshold – below the threshold, we don’t sense it
- Absolute Threshold - the minimum amount of energy needed to detect a stimulus
Method of: Adjustment, Limits, Constant Stimuli
Classical idea: there is a sharp transition in the internal state of the observer between when a stimulus can and cannot be detected.
- Method of Adjustment: The observer adjusts intensity until they can just barely detect the stimulus
- Method of Limits: The experimenter adjusts intensity up (or down) until the observer changes their response
- Method of Constant Stimuli: The observer views several preset stimulus intensities (in random order) and judges whether each is perceived or not
How an understanding of human sensory systems is helpful for psychology and human factors.
An understanding of sensory and perception can tell us about psychological factors.
Perception is the foundation for everything else: memory, learning, motor skills, emotion, motivation, social psychology, personality, and pathology.
It’s important to understand perception because we can’t always predict what people are going to see/how they are going to interpret sensory information.
Saccades are rapid, voluntary eye movements that allow us to quickly shift our gaze from one point of interest to another. There are a few reasons that our eyes do this. Which of these statements explains why we use saccades to view the world?
Only one part of our eye (the Fovea) can see in sharp focus. The eyes take in the highly focussed information in pieces, and then it is stitched together by the brain.
Stevens’ power law states that equal intensity ratios correspond to equal ratios of sensory magnitude. Which of the following is NOT true?
The law holds only for the visual system
What techniques could be used to measure a threshold for a temporal judgement?
- Two alternative forced choice
- Method of single stimuli
- Method of constant stimuli
Which is a true statement about the Vestibular System?
The vestibular system codes changes in position through displacement of hair cells in response to changes in acceleration of the body
Lateral geniculate nucleus (LGN)
The LGN both sends information to - and receives information from - the primary visual cortex.
The technique of single cell recording measures
Action potentials of a single neuron
Randot Stereotests are a type of stereo vision test used to evaluate depth perception, particularly in children and adults who may have issues with vision. Which of these can not be diagnose with a Randot Stereotests?
- Trichromacy (colour blindness)
- Amblyopia (lazy eye)
- Strabismus (Eye Misalignment)
- Stereopsis Deficiency (inability to perceive depth or three-dimensional shapes)
- Trichromacy (colour blindness)
Which of the following statements about the method of adjustment is NOT true?
- Is a psychophysical technique
- Allows the user to adjust the intensity of the stimulus
- Directly measures neural activity
- Can be used to measure thresholds
Directly measures neural activity
The term “split-brain” refers to patients in whom the corpus callosum has been cut for the alleviation of medically intractable epilepsy. Researchers in the 1960’s demonstrated that “split brain” patients were unable to name an object presented only to their LEFT visual field. What does this tell us about the LEFT or RIGHT hemispheres of the brain?
The LEFT hemisphere is used for naming objects
How would you expect the functions of the otolith organs and the semicircular canals to change in the weightless environment of space?
Without gravity, the otoliths would not be able to detect “up” and “down”.
name 4 experimental methods
- Lesion experiments
- Clinical studies
- Using perception to measure sensation.
- Using neural function to measure sensation.
How to understand the relationship between stimulus (sensation) and brain function (perception)
Real-life examples
Visual Perception:
Sensation: Light enters the eye, stimulating the photoreceptors (rods and cones) in the retina.
Perception: The brain processes these signals in the visual cortex, organizing them into shapes, colours, and movements, and interprets them as objects, faces, and scenes.
Auditory Perception:
Sensation: Sound waves enter the ear, causing vibrations in the eardrum and inner ear structures, which are converted into neural impulses.
Perception: The brain processes these signals in the auditory cortex, organizing them into recognizable sounds, such as speech, music, or noise.
Summary - the relationship between sensation and perception
the transformation of physical stimuli into neural signals (sensation) and the brain’s interpretation and organization of these signals into meaningful experiences (perception). This complex process is influenced by various factors, including attention, context, expectations, and emotions, and is supported by specialized brain regions and neural pathways.
Explain / give example of Lesions experiment
A section of an animal’s brain is lesioned (through surgery or ablation). Behaviour in the lesioned animal is then compared to an intact animal
Eg. Ferrier (1876) removed the angular gyrus of monkeys. Monkeys no longer able to drink, Ferrier concluded that the animals were blind. However vision is processed in the occipital cortext (not the gyrus)
Findings: Vision is proceeded largely in occipital cortex (not in the gyrus).
The angular gyrus is responsible for attention, self-processing, semantic information processing. Emotion regulation and mental imagery.
A complex region needed for visually guided action.
Ability to visually guided action was damaged – not likely vision itself.
describe and give example of clinical study
Patients with brain injury
Trauma (e.g., accident, war wounds).
Disease (e.g., Parkinson’s disease).
Clinical studies assess functions and anatomical extent of insult:
Neuropsychological tests
Experiments
Insight into brain function by comparing patient behaviors to behavior of non-injured person.
Example: patient DF, a woman with visual apperceptive agnosia due to injury.
What does this tell us?
Grip aperture complicated motor adjustment?
Difference in types of tasks, draw on different brain abilities?
Maybe perceptual judgment is less complicated?
The preserved visual control of grasping in is medicated by the intact visuomotor networks whereas her failure to perceive the form of objects is a consequence of damage to her ventral stream.
How does perception measure sensation
Psychophysics: investigating the relationship between stimuli and the sensations and perceptions they may produce.
what is neural function to measure sensation
Single unit recordings
Record the change in action potential of a single cell (neuron).
Record from awake, behave, behaving or anesthetized animals.
fMRI: Functional Magnetic Resonance Imaging
Measures change in blood flow.
Shows brain activity.
Shows slices of the brain.
Has been used to infer localization of function.
e.g., showing patients DF images in the fMRI seeing if the occipital lobe lights go up.
Pros and cons of lesion expirements
Pros:
Can remove specific regions
Data helps establish the idea of localization function
Cons:
As knowledge grew, discrete areas of brain function are rare
