stimulus localisation Flashcards
Give some examples of object localisation in the visual system
¥ Orienting reflex (orientation of the head and eyes to focus salient stimulus on the fovea)
¥ Smooth pursuit (following moving object)
¥ Prediction of motion during prey capture (motion anticipation)
¥ Saccadic movements during object inspection
What are saccadic movements?
When inspecting an object we look at all angles and try to get as much information as possible
Explain saccadic movements during object inspection
During natural scene perception, we move our eyes about three times each second via rapid eye movements (saccades) so that the object of interest is centered on the high-resolution fovea
What leads to disappearance of orienting reflex?
Ablation of optic tectum (superior colliculus in lower vertebrae)
Where does the orienting reflex originate?
Optic tectum (superior colliculus)
What is the function of the orienting reflex?
Alerts us to changes in our sensory environment
State the areas involved in stimulus localisation and motion processing
¥ Retina (orientation selective ganglion cells, motion anticipation)
¥ Dorsal stream in the cortex
¥ Superior and inferior colliculus
Whats the main function of the superior colliculus?
Regulation of saccadic movements
What is a consequences of a lesion of the superior colliculus?
Leads to disappearances of the orienting reflex
How are command neurons organisaed? What is their function?
Into maps, similar to retinotopic maps and send projections to layers, regulating eye movements
What does the foveation hypothesis state?
that retinotopic and topographic maps align and this is a basis for orientation reflex.
That interaction between these maps initiates orientating reflex
Explain the dorsal stream
Dorsal stream starts with V1 cortex – then v2, v3, major temporal area and then parietal area – where pathway
Interaction between where and what pathway
Which neurons are responsible for detection of motion?
Neurons in both V1 and MT cortex – some are responsible
They are able to discriminate between motion in different directions
Where is direction selectivity evident?
In the retina – mostly in typical ON/OFF cells
What is the morphology of DS cells?
Highly asymmetric – preferred direction can be guessed
Describe how you can record activity from individual cells in retina?
Good thing about retina is ganglion cells are on the top – can do sharp electrode recording and patch clamp
Where to excitatory inputs come from?
Bipolar cells
Where to inhibitory inputs come from?
Amacrine cells
Describe how you can discriminate in a ganglion cells between inhibitory and excitatory inputs
Record form ganglion cell and hold membrane potential – can discriminate between excitatory and inhibitory inputs.
i.e put membrane potential on the reversal potential for Gaba receptors then can record ampa currents. Visa versa
What defines direction selectivity?
the ratio between inhibitory and excitatory inputs
Describe what happens when stimulus moves in preferred direction?
.
stimulus moves in the preferred direction the excitatory input is much larger than the inhibitory input
What happens when the stimulus moves in null direction?
When the stimulus moves in thenul direction, the inhibitory input dominates.
There is not enough to pass threshold therefore doesn’t spike
What are retinal ganglion cells?
Neurons sending signals along the optic nerve
What is the spiking difference of a moving or flash object in a ganglion cell?
When you flash object – spiking kicks in a little bit later
Moving object- spiking rate starts earlier
Ganglion cells start spiking earlier based on position of receptive field
