Lecture 3 - Psychophysics, Characters, Color Flashcards
What did Kant believe about psychology?
Kant believed psychology would never be a science because mental phenomena cannot be observed directly by an independent observer as can be done with physical phenomena.
Context for the scientific aspect psychology
- Renaissance (14th to 17th centuries)
- shift during this period from religion-based/authoritative bestowed knowledge to empirical-based knowledge
- Enlightenment (17th and 18th centuries)
- Science was the best avenue of knowledge
- Age of reason
- Rely on the scientific method
- technology
- Gave way to the scientific revolution
- Is science always progressive?
- poison gas being used in the world wars as well as atomic bombs = horrible outcomes of science.
What was the study of (German) psychophysics
= study of the relation between the perception of a stimulus event and the physical dimensions of the
stimulus being perceived.
- German because it was created there.
- psychological part: perception
- physical part: physical dimensions (stimulus)
- originated in the work of Weber and Fechner.
Demo
- assigned researcher and subjects
- poked subject with two points, then separated the points further and further
- start at one point then to two points.
Ernst Weber’s contribution (1795-1878)
- best known for becners law
- two-point thresholds
some key terms/points:
- not absolute difference that matters, but proportional relation
- thresholds
- “Just noticeable difference (jnd)
- proposed math could be applied to psychology (mental measurement)
Demonstration of Weber’s Law [VIDEO]
- Not an absolute difference, just a proportional relation of that difference.
- holding a 2-pound weight, lift it, there is some resistance, take this weight and replace it with one that is 2.05 pounds, may notice a difference but most don’t (people typically think its the same weight)
- Instead of giving you a 2.05, gave you one of 2.20 pounds instead, most people would notice this
- threshold to noticing the change = just noticeable difference (jnd)
- in this case, the jnd is 0.20 pounds.
NEXT EXAMPLE
- starting with a 5-pound weight, then replacing it with a 5.2 (may not notice that 0.20 increase)
- if replaced with a 5.5 pound increase, you would most likely notice
- using more muscles, so more sensitive to the bigger changes
- in this case, the jnd is 0.50 pounds.
VARIABLES
intensity = 5 pounds or 2 pounds
Delta Intensity = 0.20 or 0.50.
THEORY
- Weber noticed background intermental ratio is constant
- works for tactile and auditory stimuli.
- background intensity is different in accordance with the intensity.
- predicts the linear relationship of the constant.
KHAN academy video
Ernest Weber’s measurement of mental events
- measurement and math to understand mental events
- of sensations specifically
- physical world: psychological experience is not a one-to-one ratio
- mathematical relation between mental and physical
- if you want to understand the mind, you have to know how the mind perceives stimuli.
Quotation of Fechner beliefs on measurement of the mind
“…Men and animals are bound up with the earth, and the earth-soul may be related to the individual souls of men and animals as the earth-body is to their bodies …all souls are part of the highest, all-embracing soul, whose life and reality is manifested in the casual law; and the causal law is the principle of all interconnection and all order in the universe.”
- religious beliefs > impacted how/what he said and thought about things.
Gustav Fechner (1801-1889)
- Wanted to resolve the mind-body problem and materialism (disprove materialism),
- pursues psychophysical parallelism through psychophysics
- experimental psychologist?
- psychophysics to tackle mind-body question
- measure psychological sensations and physical stimuli
- sensory thresholds
- created the first book in experimental psychology
Fechner’s elements of psychophysics
- use jnd as a unit of measurement
- absolute threshold (when you first start to notice a difference) = as the intensity increases above the threshold, a person experiences a jnd (then another, and another)
- difference thresholds
- sensations could be precisely measured.
- created psychophysics
- a systematic method still used today.
What are the three methods for making psychophysical measurements.
(1) Method of just noticeable differences.
- measure both the absolute threshold and the differential threshold.
- In its simplest form the method involves increasing or decreasing the magnitude of a stimulus until the subject detects a change.
(2) Method of right and wrong cases.
- This procedure is also called the method of constant stimuli because it relies on a set of pre-selected stimuli that vary in magnitude.
These stimuli are presented to the observer in a random order, and it is the observer’s task to say whether or not each one is perceptible.
- The absolute threshold corresponds to that value of the stimulus which the observer reports being able to perceive 50 percent of the time.
(3) Method of average error
- The method of average error is similar to the method of limits in that it involves one stimulus that does not vary and another stimulus that does.
- However, in this case, the variable stimulus is under the control of the observer and is not varied by the experimenter.
- For example, the observer could be shown a line and asked to adjust a variable line so that the two appear equal in length.
- This is called the point of subjective equality. There will almost inevitably be some error in the subjects’ judgments, the average of which constitutes the difference threshold.
Timeline for Charles Bell, Francois Magendie, and Johannes Muller
Charles Bell, 1811:
- Self-publishes pamphlet focused on anterior roots
- untested assertions in the pamphlet
- Scottish anatomist
Francois Magendie, 1822
- Publishes a 3-page article on an experimental study showing posterior roots (in the spinal column?) are responsible for sensation and anterior roots for movement.
- did not have much formal education, father was a surgeon, had an in.
- implications: severed some of these connections in puppies
- single cell direction and there are different regions in the brain that are responsible for movement.
- his experiments caused advocacy for anti-animal cruelty.
Johannes Muller, 1831
- Conducted experiments in frogs. Introduced a highly reproducible experiment.
- showed the same effect as Francois.
Müller and the law of specific energies of nerves
- an “impression made no two different nerves of sense, though with the same instrument, will produce two distinct sensations (Bell, 1811)
- different nerves have different qualities
- For example: the tongue - some nerves on your tongue are for taste, some for touch.
- one stimulus can cause two sensations
- different stimuli can cause the same sensation i.e. hitting your eye of something or seeing light from touching your eyelid.
- we are only aware of what is in our world based on what is filtered through our nervous system.
- the doctrine of 10 related principles in the textbook he published, the authoritative textbook of the 1700 - law of specific energies.
- Müller: The nervous system acts as a filter between people and the external world
- published Handbook on Human Physiology (1840)
Hermann von Helmholtz (1821-1894)
- studied informally with Muller; befriended Ernst Brucke, Emil du Bois Reymond, and Karl Ludwig
students were challenging him on these aspects:
- vitalism = idea that there exists a life force (Muller believed in vitalism, students did not)
- materialism = the only reality is physical matter
- students were proponents of materialism.
- Helmholtz was a materialist.
- Helmholtz’s Theory of Colour Perception
- Christine Ladd-Franklin’s Evolution Theory of Colour Perception
Reaction time (Du Bois’s work that impacted) and how Helmholtz measured it.
- Du Bois-Reymond - electrochemical waves (thought we can measure this)
- Hemholtz created this galvanometric stopwatch used to measure the stimulus in the frog legs
- stimulus to response time frog’s leg
- record the time from stimulus to response 83ft/second measured
- did this with human participants - longer to get to the toe than the thigh
- Muller - believed that nerve impulses travel too fast to measure
- Helmholtz told students that the electrochemical wave of a nerve impulse can be measured - if it goes slow enough we could measure it.
