Perception Flashcards
What was the assumption about mind and body until the mid 1800’s?
an assumption that the mind and the body are separate from each other
What did Gustav Fechner reveal about the mind and body in the 1850’s?
the mind and body are not independent and so the mind can be studies by measuring the relationship between changes in physical stimulation and a person’s experience
What was proposed in ‘elements of psychophysics’, published in 1860 by Fechner?
proposed a number of methods to study the relationship between mental and physical. this included the proposal of three techniques to measure thresholds
Define Psychophysics:
the scientific study of relationship between physical stimulus and perceptions evoked by it
Define Absolute Thresholds:
measures the minimum of a stimulus that can be perceived by one of our senses
Define Difference Thresholds:
measures the smallest difference between two stimuli a person can detect
What is the steps of psychophysics deconstructed?
-physical stimulus (how do we select and present the stimulus)
-task (what does the participant have to do)
-measure (how do we categorise behaviour)
What are the three methods to measure thresholds?
method of limits, method of adjustment, method of constant stimuli
How is the threshold determined in the Method of Limits?
experimenter presents stimuli in ascending or descending order and determines the cross over point where perception changes. the threshold is the average of the cross over points
How is the method of adjustment carried out and how effective is the method?
the participant adjusts the stimulus intensity. It is a relatively fast method but it is frowned upon for it’s accuracy
What is the most accurate method of measuring threshold and why?
Method of constant stimuli because it involves more observations and the stimulus is presented in a random order to reduce order and expectation effects.
Describe the method of constant stimuli and how the threshold is reached:
the experimenter is presented stimuli of different intensities in a random order. participants indicate their perception, the stimulus is chosen so that the weakest is never detected and the strongest is always detected. The threshold is the intensity at which stimulus is detected 50% of times
How many intensities are typically involved in the method of constant stimuli?
5 to 9
What is a quick solution to the expectations of subjects and order effect?
Forced Choice Procedures (Fechner)
What do Forced Choice Procedures entail and how is the threshold determined?
stimulus is presented side by side and participants choose which side contains the stimulus (ie. grating) until it is too faint to see. Due to the guessing chance, if participants are unable to see the grating at all they should obtain 50% correctly. The Threshold is therefore determined at 75% correct
Explain the difference between 2AFC and 2IFC in the Forced Choice Procedure:
2AFC: the stimulus is presented at the same time
2IFC: the stimulus is presented one after another
What is the up-down method that measures perception?
Adaptive Staircase Procedure
How is the Adaptive Staircase Procedure carried out and how is the threshold reached?
intensities that are included in the threshold are presented. the procedure begins with perceivable stimulus and if correctly identified the intensity is decreased until an error occurs and the intensity is increased again. The threshold is determined by averaging over the transition and reversal points
What are three classical psychophysical tasks used to determine thresholds?
-detection: is the stimulus there?
-discrimination: which stimulus is stronger?
-matching: adjust the stimuli so they look/sound/feel the same
What is weber’s Law?
The ratio between the difference threshold and the intensity of the standard is constant
What does the difference threshold depend on?
the size of the standard stimulus
What is the accuracy of Weber’s Law determined by?
As long as the stimulus intensity is not too close to the absolute threshold
What does Weber’s Fraction depend on?
the sensory dimension measured as the value of standard stimulus is different between dimensions
How is perception measured above threshold?
Magnitude Estimation (Stevens, 1957)