Ch. 4 Flashcards
Proprioception
Body parts relative to each other
Exproprioception
body and its various parts relative to environment
Exteroception
visual layout and relative position of objects in space
Iris activity indicate
ANS function
Cone cells
fovea
high levels of illumination; day vision
Many sensory nerve fibers
Rod cells
peripheral retina, nearest lens
poorly lit conditions; night vision
Single sensory nerve fiber
Visual Processes
Light waves are transducer into electrical impulses by rod and/or cone cells
Transmission to the Brain
Electrical impulses leave the eye via the optic nerve
- Optic tracts arise from the optic nerve- relays impulses to the thalamus
- Partial crossing at optic chasm- allows three dimensional viewing, binocular viewing
Transmission to the Brain (2)
Most information travels via thalamus to the primary visual cortex: organizes the scene; contrast and form
Some info goes to the superior colliculus (SC) in midbrain: Reflexive control of eye and head movements. Also plays an important role in attention and visual perception / integration with other sensory information
Visual association areas: final perception of the external world
Accommodation
Ability of lens to focus
Declines with age
Visual Acuity
Discern detail
Factors affecting visual acuity include contrast, lighting, time, motion, age, color, attentional demands
Dynamic Visual Acuity
More important in sports
Improves from ages 6-20; vision becomes adult-like between ages of 10-12 but then begins to decline
DVA can be improved in adults with training
Eye movements
Involuntary: vestibular ocular reflex optokinetic reflex Voluntary: smooth pursuit saccades vergence
Vestibulo-Ocular Reflex
The automatic generation of eye movements from movements of the head
Signals from he semicircular canals are sent directly as possible to the eye muscles
Using these direct connections, eye movements lag the head movements by less than 10 ms, one of the fastest reflexes in the human body
Optokinetic Reflex
Allows the eye to follow objects in motion when head remains stationary
To help achieve a stable retinal imagine
Complimentary to the VOR
Has a longer latency and most responsive at lower frequencies (0.1 HZ) of head movements
Smooth Pursuit
Keeps moving object fixed on fovea
Speed voluntarily determined
Saccades
Quick shifts
Angular distance between objects determines speed
Vergence
eyes move in opposition
Convergence
Divergence
Two visual systems?
Two structurally distinct pathways, leading to different areas of the brain suggest existence of two visual systems:
Focal system: what
Ambient system: where
Focal System
Responsible for identification of objects in the center of the visual field
Involved the fovea of the eye; high visual acuity
Best in bright light
Involves conscious though
Pathway leading to primary visual cortex is responsible for this type of visual processing
Ambient System
Used for detecting space around the boy while providing information about where objects are in space
Involves the entire retina
Best in dim light
Involves subconscious processing
Helps prevent collisions while walking busy street
Two Visual Systems working together
Appear to work in parallel in most movement situations:
Focal system: assists in identifying objects in the space
Ambient systemL is used to locate objects in space at a subconscious level and orient the body during movement
Two systems allows us to attend to different forms of visual input at the same time
Theories of Visual Perception
Two different theories for Visual Perception:
Cognitive or Indirect theory
Ecological or Direct theory
Indirect Theory
(Cognitive)
Visual perception is based on one’s understanding of the environment through deductive internal processes
Requires cognitive activity, thus perception is indirect - NOT directly apparent from the visual scene
