PSY 2104 Study Guide - Fall 2018, Comprehensive Midterm Notes - Visual System, Retina, Fovea Centralis
12 Oct 2018
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PSY 2104
MIDTERM EXAM
STUDY GUIDE
Fall 2018
What is signal detection theory and why is it important?
What is the anatomy of a neuron and the basic structure of cortex?
How can we study sensation and perception at a neural and behavioral level?
Our perception is our brain’s interpretation of our environment.
Evolution has honed our sight, sound, touch, smell taste, tilt/rotation for survival
Plato’s Cave- Our understanding of reality is biased by the limitations of our senses.
Thresholds and Detection
• Consider hearing a phone call when you are taking a shower
• If the phone is far away or quiet, you may not be certain you heard the call.
• Your confidence is influenced by the volume of the phone (signal) versus to volume of
the shower (noise)
A Few Thresholds
Two-point touch threshold
• The minimal distance between two tactile stimuli in which they can be distinguished
from each other
Just Noticeable Difference Threshold
• The minimal distance between two stimuli that can be correctly distinguished from each
other
• Discrimination between two stimuli
Absolute Threshold
• Minimal amount of stimulation necessary for a person to detect the stimuli 50% of the
time
• Discrimination between stimulus presence or absence
Ernest Weber (1795-1878)
Weber observed ability to denote change (just noticeable difference, JND) relative to physical
intensity of stimulus
• Weber Fraction: if an individual was just able to tell tell difference between
• 40 and 41 gram object, they would also be just able to discriminate 400 from 410 gram.
• Fixed ratio for difference senses (weight 1:40, visual detection of length 1:100, etc).
• As we will see, Weber fractions not precisely right, but a good rule of thumb.
Gustav Fechner’s Law
• Fechner’s Law: Introspective Sensation (S) increases logarithmically with objective
physical intensity
o S = k log R
Stanley S Stevens (1906-1973)
Refined Fechner’s law
• Some perceptual estimates linear
find more resources at oneclass.com
find more resources at oneclass.com
o Something twice as long looks twice as long
• Some saturate
o Object twice as bright is perceived as being only a bit brighter
• Some exponential
o Slightly more intense electric shock feels much stronger.
• Steven’s Power Law: Introspective sensation (S) depends on objective intensity (R) as
well as a modality specific constant (a) and exponent (b) S = aRb (b is an exponent)
Signal to Noise
Car radios are a good example of SNR
• When we are near the radio transmitter, the signal is crisp (high SNR)
• As we drive further the signal degrades. Eventually, it becomes hard to understand what
the radio announcer is saying (poor SNR).
Signal to Noise
Many real world situations are noisy
• Photography is a good example:
o Our photos have good SNR if the light is bright and we are photographing a static
object (slow shutter speed)
o We will compromise SNR if we want to freeze motion (fast shutter speed)
o We will compromise SNR if taking a photo in a dark room (need to boost
amplification)
• It is easy to discriminate events if there is high signal to noise, but harder if there is a lot
of noise.
o Again, think of trying to determine if the phone is ringing when you are in the
shower. Harder to discriminate if the phone is quiet (low signal) or if the shower
is loud (high noise).
Signal Detection Theory
• It is hard to detect events when there is poor SNR
• Consider hearing the phone ring when we are taking a shower
• In these threshold situations, we are not 100% confident
o If we decide the phone is ringing, we will either be correct (hit) or incorrect (false
alarm)
o If we decide the phone is not ringing we will either be correct (correct rejection)
or incorrect (miss).
• In these situations, we will always make mistakes, but we can choose a criterion to
influence the kind of mistakes.
Criterion
• In court case, accused is either guilty or innocent. Will be found guilty or innocent.
• In ambiguous cases, court will sometimes make mistakes, but we can choose a criterion
for the burden of proof that biases the type of mistake we are likely to make.
o Civil case: ‘preponderance of the evidence’. Ensure we are likely to convict guilty
o Criminal case: ‘beyond reasonable doubt’: rather let guilty free then send innocent
person to jail.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Our perception is our brain"s interpretation of our environment. Evolution has honed our sight, sound, touch, smell taste, tilt/rotation for survival. Plato"s cave- our understanding of reality is biased by the limitations of our senses. Thresholds and detection: consider hearing a phone call when you are taking a shower, your confidence is influenced by the volume of the phone (signal) versus to volume of. If the phone is far away or quiet, you may not be certain you heard the call. the shower (noise) Two-point touch threshold: the minimal distance between two tactile stimuli in which they can be distinguished from each other. Just noticeable difference threshold: the minimal distance between two stimuli that can be correctly distinguished from each other, discrimination between two stimuli. Absolute threshold: minimal amount of stimulation necessary for a person to detect the stimuli 50% of the time, discrimination between stimulus presence or absence.
