Sensory Systems and Perception Flashcards
what are ganglion cells
cells in the retina that have a receptive field which act as ‘edge detectors’
some ganglion cells can be
- excited by light inside the receptive field and
- inhibited by light outside the receptive field
integrate patters of lightness over and area
identifying edges by indicating if a pattern of lightness within an area is different to that in an adjacent area
components of the eye
photoreceptors - pick up points of light
‘Lens’ that inverts the image and projects it back to the receptors
Fovea
what does selective focus mean
- we don’t see everything perfectly
rather focus on what we really want to see
like camera focusing on a subject and blurring surroundings
Accentuating the middle of the visual field -
the Fovea
what is it?
- exact centre of the visual field where light rays enter the eye straight along the axis of the eye
- represents the location the eye is pointing when you look at something
- greatest concentration of photoreceptors
- 2 types of photoreceptors
Accentuating the middle of the visual field -
the Fovea
CONE photo receptors
- colour vision
- high acuity ( can see very fine details as they are densely packed in the fovea)
- work primarily in bright light (daylight ‘photopic” vision)
Accentuating the middle of the visual field -
the Fovea
ROD photo receptors
- black and white vision
- low activity (widely spaced throughout the retina , more in the peripheral visual field)
- Work well at night (night time ‘scotopic’ vision
depth perception - 2 eyes , 2 images
- contralateral control
- nerve cells cross over at the optic chasm (midbrain)
- Travel to lateral geniculate nucleus of thalamus (LGN) then back to occipital cortex at the back of the brain
- with two images you can triangulate the location of the object
Ascending visual system – intelligent filters for identifying ‘stuff’
three types of cells in the primary visual cortex - external occipital lobe
integrating information from ganglion cells
simple cells
- respond to edge at a particular orientation in a specific part of the visual field
- primarily respond to oriented edges and gratings
Complex cells
- responds to edges at a particular orientation but falling anywhere within a wider field
- may also respond to direction of motion
- receives input from a number of simple cells
hypercomplex cells
- respond to a line which ends within the receptive field
- AKA end-stopping cells
Ascending visual system – intelligent filters for identifying ‘stuff’
Higher levels of the visual system
temporal lobe
- detects combinations of lines and edges (square or cone shapes
colour + orientation combinations
object detectors
Ascending visual system – intelligent filters for identifying ‘stuff’
agnosia
the inability to recognise objects
prosopagnosia -
specific inability to recognise faces
Higher system for identifying where the objects are
damage to the parietal lobe …
causes problems of spacial awareness
eg. visual neglect
Higher system for identifying where the objects are
visual maps
information is distributed in multiple parallel visual maps
Retinotopic - mimics the layout of the visual field
often centre-weighted ( central 5 degrees represented most strongly)
maps only indicate where things are in the visual field
Higher system for identifying where the objects are
stabilisation of vision
what happens when you move your eyes?
other connections exist with higher cortical levels , including frontal association cortex
tell your where your eyes are pointing to make an internal map of where things are located
