Cortical Processing of Visual Information Flashcards
What is the orienting reflex?
Orientation of the head and eyes to focus salient stimulus on the fovea
What is smooth pursuit?
Following of a moving object
What is saccadic movement during object inspection?
The movement of the eyes in a way that particular features of the object are projected onto the fovea
Ablation of the optic tectum leads to the _____ of the orienting reflex
Disappearance
Superior colliculus
Receives input from ganglion cells, auditory system and somatosensory system
Integrates information from different sensory modalities
What is the main function of the superior colliculus?
Regulation of saccadic movements
What is a retinotopic map?
Organisation whereby neighbouring cells in the retina feed information to neighbouring places in their target structures (LGN, SC, cortex)
Foveation hypothesis
States that interaction between retinotopic maps of the visual neurones and topographic maps of the motor neurones initiates orienting reflex
Why is foveation hypothesis invalid?
Interaction between the maps seems to be indirect
Lateral geniculate nucleus
6 layers
Monocular input
Layers alternate input from one eye
Organised retinotopically
Which layers receive information from the contralateral eye?
1, 4 and 6
Which layers receive information from the ipsilateral eye?
2, 3 and 5
Which layers receive information from M cells?
1 and 2
Which layers receive information from P cells?
Layers 3 - 6
What is scale invariance?
Being able to recognise an object even when they have been scaled to a size which we haven’t encountered before
What is orientation invariance?
Being able to recognise objects even when they are in an orientation which we haven’t previously experienced
Hierarchical model of object recognition (simplified model)
Detection of edges
Detection of combination of edges and contours
Detection of object parts (eg. face)
Detection of objects from one point of view (a person from the front)
View-invariant object detection (particular person, a car)
Categorisation (a human, an animal, a vehicle etc)
Along the ventral stream, the complexity of responses of neurons _____, as does the size of the receptive field of the neurons
Increases
Key features of the cortical structure
Layering Columns (ocular dominance, orientation, direction) and blobs
Ocular dominance columns experiment
Inject radioactive proline in one eye
Or inject radioactive glucose in the cortex and stimulate one eye
Labelled column receives information from one eye, and unlabelled column from the other
Orientation column
Each column, neurons respond to edge in a particular orientation
Each column is a different orientation
Blobs
Contain neurones which are specifically tuned to process information about colours
What is a hypercolumn?
Three types of columns together
Unit which can process all the useful information for object recognition
Hubel and Wiesel
Inserted electrodes into cats brains in different cortical areas (mainly D1)
Made cats look at screen and look at visual stimuli
Three types of cells in V1
Simple
Complex
Hypercomplex
Complex cells response
Responds to a bar in certain orientation when presented anywhere in the receptive field
Simple cells response
Responds to a bar in a certain orientation when presented in the centre of the receptive field
Hypercomplex cells response
End-stopped complex cell
Responds to a bar in a certain orientation anywhere in the receptive field
Stops responding when the bar goes out of the receptive field
