object recognition

Question 1

examples of object recognition in nature

Answer 1

echolocation
- e.g bats finding water = smooth surface targetted, rough surface avoided

electroreception
- fish create electric field and detect with electroreceptors and can detect any objects nearby

Question 2

what is orientation invariance

Answer 2

being able to identify an object when it is at a different angle

Question 3

what is scale invariance

Answer 3

being able to identify an object when it is a different size

Question 4

heirarchical model of object recognition

Answer 4

categorisation
view-invariant object detection
detection of objects from one perspective
detection of object parts
detection of combination of edges and contours
detection of edges

Question 5

lesions where decrease ability to recognise objects?

Answer 5

Lesions in inferior temporal cortex

Question 6

role of lateral geniculate nucleus

Answer 6

sends information to primary visual cortex at back of brain

Question 7

structure of lateral geniculate nucleus

Answer 7

• 6 layers
• recieve input from parvocellular (resolution) and magnocellular cells (motion)
• first 4 = PC, last 2 = MC
• layers recieve different inputs from contra and ipsilateral eyes

Question 8

what brain structure is linked to the ventral visual pathway

Answer 8

inferior temporal lobe

Question 9

key structural features of LGN

Answer 9

• 6 layers of neurones with different functions
• columnar structure allows occular dominance
• orientation and direction
• blobs

Question 10

what are blobs

Answer 10

• parts of brain with specific properties
• contain neurones processing information about colour
• receive info from parvocellular cells of LGN

Question 11

what is the ventral pathway

Answer 11

figures out WHAT the object is
information that leads to the temporal lobe, which is involved with object and visual identification and recognition.

Question 12

what is the dorsal pathway

Answer 12

finds out WHERE the object is
leads to the parietal lobe, which is involved with processing the object’s spatial location relative to the viewer and with speech repetition.

Question 13

what is lateral geniculate nucleus

Answer 13

structure in thalamas

Question 14

what layers of LGN are magnocellular and parvocellular cells?

Answer 14

The top four are parvocellular layers, two layers from each eye. Parvo (small) LGN cells receive inputs from (small) midget ganglion cells.

The bottom two are magnocellular layers, one layer from each eye. Magno (large) LGN cells receive inputs from (large) parasol ganglion cells

Question 15

where do P and M ganglion cells send their axons?

Answer 15

Retinal P ganglion cells send axons to a parvocellular layer, M ganglion cells send axons to a magnocellular layer

Question 16

which eyes send info to which layers of LGN?

Answer 16

the eye on the same side (the ipsilateral eye) sends information to layers 2, 3 and 5

the eye on the opposite side (the contralateral eye) sends information to layers 1, 4 and 6.

Question 17

areas sending info to LGN

Answer 17

retina, visual cortex, superior colliculus, pretectum, thalamic reticular nuclei, and local LGN interneurons.

Question 18

what is centre-surround organisation

Answer 18

• Characteristic found in retinal ganglion and bipolar cells where the centre sends one type of signal, and the ring around the centre sends another.
• ON stimulates neuronal responses and OFF supresses neural responses.

Question 19

role of the primary visual cortex

Answer 19

• LGN sends most of its axons there so it is the first processing area in cortex
• once V1 processes LGN info, it sends output to other visual cortices e.g V2,V3
• located in calcarine sulcus in medial occipital lobe

Question 20

organisation of primary visual cortex

Answer 20

• columnar orientation
• columns respond to different stimuli
• chunks of cortex about 1 mm square by 3 mm thick that contains neurons, all with same receptive field location, but with all different orientation selectivities, direction selectivities, both (left- and right-) eye dominances represented.

Question 21

what determines orientation of receptive field in simple cells

Answer 21

• 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

Question 22

how are receptive fields of simple cells elongated

Answer 22

each simple cell sums inputs from LGN neurones to build elongated receptive field responsive to bars and edges

Question 23

features of simple cell receptive fields

Answer 23

• respond best to elongated bars or edges
• orientation selective
• separate ON and OFF subregions
• length summation

Question 24

features of complex cell receptive fields

Answer 24

• orientation selective
• no separate ON/OFF regions
• binocular
• length summation

Question 25

hypercomplex/end stopped cells

Answer 25

larger receptive field that fires when objects are anywhere in region
if bar goes away from receptive field, stimulates inhibitory cells

Question 26

how are extremely complex shapes processed?

Answer 26

• grandmother/jennifer aniston neurones
• Neurone/group of neurones responds to images of a particular object (subject) in any orientation and scale

Question 27

issues with hierarchical model of object recognition

Answer 27

• Still poor in scale- and orientation invariance
• doesnt take into account feedback from higher cortical areas
• needs experimental validation which is difficult because you need to record pre and postsynaptic responses