Lecture 5 & 6 Flashcards
What is the visual feild
Everything you can see at a given moment
How is the visual field created
Each eye’s retina captures an image, and the brain combines both images
Optic chiasm
Base of the brain
Optic nerves meet and partially cross
Right visual field to left hemisphere
left visual field to right hemisphere
NASAL (Inner) cross over
TEMPORAL (outer) don’t cross
Ipsilateral and contralateral
Contra: crossing over
Ipsa: same side
What is the full pathway of visual information
RETINA (rods and cones) –> OPTIC NERVE –> OPTIC CHIASM –> LGN —> PRIMARY VISUAL CORTEX (v1)
What is the LGN
Lateral geniculate nucleus
> part of the thalamus
EARLY Visual processing,
relay station to V1
Primary Visual Cortex (v1)
in the OCCIPITAL LOBE
> detects edges, orientation, and spatial features
Acuity
The ability to distinguish fine details, limited by density of photoreceptors
What are the types of acuity?
RESOLUTION ACUITY: Smallest spacial detail that can be detected (cycles per degree)
GRATING ACUITY: The ability to distinguish fine patterns (e.g., B&W bars)
SNELLEN ACUITY: 20/20 vision etc. (letters)
MINIMUM VISIBLE ACUITY: Smallest detectable object against a background
MINIMUM DISCRIMINABLE ACUITY: Perceiving slight differences in spatial position (HYPERACUITY)
What is the Retinal convergence and sensitivity/acuity tradeoff
High convergence= high sensitivity (LOW LIGHT)
Low convergence = Low sensitivity (FINE DETAILS)
What is spatial frequency?
Number of cycles of a patter per unit of visual angle
LOW SF: Coarse details; large blurry objects
HIGH SF: Fine Details (sharp edges, textures)
What is Fourier Decomposition
Any image can be broken down into a sum of sine wave gratings with different frequencies, which the brain will process separately
> Efficiency of recognizing objects
How are fourier decomposition and Spatial Frequencies related
Fourier decomposition separates an image into multiple spatial frequency layers
Contrast Sensitivity
Ability to detect changes in contrast at different spatial frequencies
CSF Curve
Plots contrast sensitivity against spatial frequency.
What factors affect the CSF
> Retinal Position (sensitivity high in the fovea)
Light adaptation (better contrast in bright light than dim light)
Temporal Frequency (Faster moving stimuli need low contrast to be detected
Age and development (infants low contrast sensitivity)
Primary Visual Cortex
Analyzes basic features of visual stimuli; orientation, movement, spatial frequency
V1 Simple, complex, and LGN cells
v1 simple: bars of light spec. orientation
v1 complex: motion and orientation
LGN cells: spots of light
The psychologists electrode (visual adaptation)
nuerons reduce their response after prologed exposure
eg retinal fatigue, neutral distortion with high contrast etc.
Infantile spatial vision
Newborns have poor aqcuity low contrast sensitivity
Techniques for studying infant vision
Preferential looking (patterns over plain)
Visual evoked potentials (measure brain responses to visual stimuli
