BMS248 Lecture 6 - Object Recognition (Ventral Stream) Flashcards
What are the principles of the hierarchical model of object recognition? (2)
As you go along the ventral stream there is:
1. An increase in receptive field size of neurons
2. An increase in stimulus complexity and therefore the complexity of responses of neurons
Lesions in what decrease the ability to recognise objects?
How is this studied?
Inferior temporal cortex
Studied by modelling and electrophysiology
Where does the LGN receive input from?
Retinal ganglion cells - 1:1 connection via optic nerves (LGN projection neurons)
How many layers are there in the LGN?
What cells are present?
How are the layers organised?
6 layers - alternate input from each eye.
Segregation of M (1,2) and P (3,4,5,6) ganglion cells.
Retinotopic organisation - retina, LGN, and cortex are all layered
Where does most of the input to the LGN come from?
From the Cortex (60%) - back propagation
Rest from retinal ganglion cells
What is the organisation of the ventral stream (what)?
- P-Ganglion Cell (retina)
- LGN Parvocellular pathway
- V1 cortex (primary visual cortex)
- V2 cortex
- V4 cortex - colour
- Inferior temporal cortex - form/object recognition
(Hierarchical model)
What are two key features of cortical structure?
- Layering
- Columns
What are the 3 types of columns in the cortex?
- Ocular dominance columns - layer 4 of V1 cortex
- Orientation (direction) columns
- Blobs (colour)
Where do ocular dominance columns receive input from?
Each column receives inputs from either ipsilateral or contralateral eye exclusively - from the LGN
What do Blobs process and where do they receive their input from?
Process information about colour
Receive input from parvocellular cells of the LGN
What do the different orientation columns respond to?
Different V1 neurons respond to a bar oriented in a specific direction
What is a “simple cell” in the V1 cortex, its receptive field, and what layers are these found in?
Simple cells respond to a bar oriented in a specific direction in the CENTRE of the receptive field - they can do this as they have larger and more elongated receptive fields compared to RFs in the retina and LGN.
Simple cells are localised in layers 4 + 6
What is the circuit mechanism of a simple cell?
Centres of the receptive fields of all neurons projecting to the same simple cell are oriented along a line. Orientation of this line determines the orientation of the receptive field of the simple cell.
What is a cortex complex cell, what does it respond to, and where are they found?
Complex cells respond to a bar in certain orientation positioned ANYWHERE in the receptive field.
Complex cells are localised in layers 2, 3 and 5
What is the circuit mechanism of a complex cell?
Complex cells collect information from many simple cells with similar orientation
