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
Direct Theory
Visual information can be directly extracted from the environment
The optic array provides all the necessary information to guide movement
Does not require any intervening cognitive processes to determine meaningfulness
Which theory is best?
Research supports both theories:
Indirect theories best to explain movement governed by a set of rules (sport)/dynamic environment or situations with anticipation
Direct theories best in stable environments/standing upright, moving through space, interception a moving object in a stable environment
Visual Guidance of Action:
Indirect theory assumption
Indirect theories assume that the visual system provides system provides predictive information early in an objects flight by which to determine when to initiate action
Visual Guidance of Action: Direct theory assumption
Assume that visual information is continuously used to monitor the object’s flight using optic tau
Time-to-time contact information
Visual Guidance of Action: Visual Dominance
over all other sensory systems as source of sensory feedback, even when it provides inaccurate information
Can have a negative effect: sensory conflict, situation requiring a rapid response; rely less on somatosensory cues
Vestibular Apparatus
The VA constists of Utricle, Saccule, and Semicircular canals
Utricle: horizontal acceleration of head
Saccule: vertical acceleration of head
Semicircular canals: angular acceleration
Contributes to static and dynamic equilibrium and resolution of sensory conflicts
Ascending Pathways
From vestibular nuclei to thalamus, cortex, cerebellum, spinal cord and oculomotor nuclei
Spatial orientation
Descending Pathways
From vestibular nuclei to spinal cord
Postural control
Vestibular Contributions to Actions
Works collaboratively with the visual system and the somatosensory system to :
maintain posture (reflexive role in balance)
stabilize vision when the head is moving
