Lecture 7 Flashcards
what information goes to each part of the brain from the eye
Contralateral– information from the nasal part of the retina crosses to the other side of the brain, such that the left visual field is seen by the right hemisphere and vice-versa
what does LGN stand for
Lateral Geniculate Nucleus
what is the LGN
where the information passes through to get to the brain (from vision)
there are 2, the left and the right
what are the Types of layes in the LGN
Magnocellular (1 and 2)
Parvocellular (3-6):
what is the Magnocellular (1 and 2) layer
Large cells, bottom two layers. Receive input from M ganglion cells. Respond best to large, fast-moving objects
what is the Parvocellular (3-6): layer
Smaller cells, top four layers. Receive input from P ganglion cells. Respond best to fine spatial details of stationary objects.
what are the Properties of the LGN:
Controlateral representation: left LGN recieves info from the right visual field and vice-versa.
Each LGN layer receives signal from one eye only.
Within each layer of the LGN, the neurons are arranged in a retinotopic map of the visual field. In other words, RGCs (receptive ganglion cells) with adjacent receptive fields connect to adjacent neurons in the LGN (AKA each spot in retina has a corresponding place in the LGN)
what is another name for the Primary visual cortex
striate cortex
what are Two important features of striate cortex
Retinotopic mapping
Cortical magnification
what is Cortical magnification
Dramatic scaling of information from different parts of visual field
Proportionally much more cortex devoted to processing the fovea than to processing the periphery (aka lots more space in the cortical magnification dedicated to the fovea than periphery)
what is Retinotopic mapping
each part in your visual field corresponds to a place in the straits cortex
Why sine gratings?
Any black-and-white image can be described in terms of a weighted combination of different : (there are 4 properties)
aka every image can be decomposed into what?
frequencies,
contrast,
phases, and
orientation
Low frequencies = broad outline
High frequencies = details
Retinal ganglion cells are sensitive to what
1) frequencies, 2) contrast, 3) phase, but not 4) orientation…
is it possible to detect the orientation fo an image with just one ganglion cell
no,
By combining information from SEVERAL retinal ganglion cells, it is possible to detect the orientation of lines.
what is the Tilt after-effect
We have different populations of neurons that specialise in certain frequencies and orientations.
Adaptation: Looking at a pattern of stripes for a certain time will “tire” the neurons and shift the balance in the opposite direction.
-> Note: this also implies that orientation is encoded by a population of neurons
(this is the example with the red dot embedded in the black and while lines)
define Sensation
Sensory receptors activated after receiving a specific input
define Perception
Interpretation of the sensory input
define Visual Sensation:
light activating photoreceptors (rods and cones)
in the retina
define Visual Perception
how the environment is consciously perceived after organization and interpretation of the retinal input
Visual Perception occurs at what level (where)
This occurs at the level of the cortex and involves both bottom-up and top-down processes including attention, context and preconceived ideas about the world.
how does sensation get translated into perception
via the visual pathway
how does the visual pathway/system work
From the retina, the visual information travels to the lateral geniculate nucleus (LGN) in the thalamus.
From the LGN, neurons project either to subcortical structures or to the visual cortex.
