What is Echolocation?
a physiological process for locating distant or invisible objects by means of sound waves reflected back to the emitter by the objects
How does a bat use echolocation with water surface?
Water surface is smooth so the bat can sense sounds in all directions but the only one that will come back is from behind because every other wave reflected goes elsewhere
This allows bats to survey water surface by using echolocation
How does an electric fish use echolocation?
- create an electric field around them and have sensors to detect
- If object in close proximity there will be changes in the electric field
- If object is big they can decide to swim away or if its small they can bite it
What is scale invariance?
recognising an object at a different size
What is a centre question in understanding object recognition?
what features do we identify to specific objects e.g. stick men and women
What is the hierarchy of object recognition?
- Detection of edges
- Detection of combination of edges and contours
- Detection of object parts i.e.face
- Detection of objects from one point of view
- View-invariant object detection
- Categorisation (human, animal etc.)
What increases as object recognition hierarchy increases?
- Complexity
- The receptive field size of neurons along the ventral stream
What are present at the top of the visual pathway?
Neurons that respond to more complex features e.g. the presentation of certain objects
Describe the structure of the Lateral Geniculate Nucleus (LGN)
- Contains 6 layers
- All layers receive input from the ganglion cells but two of them receive information from magnocellular cells and 4 of the layers receive information from parvocellular cells
- Layers alternate with visual input from left/right eye
- Ganglion cell axons make 1:1 connections with LGN projection neurons
What is the difference between parvocellular and magnocellular cells?
Parvocellular = object recognition
Magnocellular = stimulus recognition and speed etc.
Where does most of the input to the LGN come from?
V1 cortex, 60% of input comes from the V1 cortex rather than the retina
Where does information go once its been in the LGN?
V1 cortex where it can go into the Dorsal root ‘where’ pathway or the ventral root ‘what’ pathway
Describe the cortical layers
- 6 of them too with ocular dominance columns and orientation columns
How are ocular dominance columns found?
- injecting radioactive substances into one of the eyes you see alternate layering
- radioactive part showing receives input from one eye and the other receives input from the other eye
- can also inject radioactive glucose in the cortex and stimulate one eye with light
What is a Blob?
- Stained by cytochrome oxidase
- Process information about colour
- Receive input from Parvocellular cells of the LGN
- Not orientation-selective
What are Columnar orientation columns?
Different neurons respond to different orientations
- Within each orientation column, neurons have similar orientation preferences, meaning they respond most strongly to visual stimuli with specific orientations
- Neurons within orientation columns detect specific visual features (edges or lines) aligned with their preferred orientation.
Where are the columnar orientation columns and how can you experimentally test them?
- In v1 cortex
- Stimulating visual system using recording electrode when exposed to certain stimulus
- Turning the orientation leads to less AP fired in certain parts of the brain
- The cells that fire AP are called ‘simple cells’ located in layers 4 and 6
What are simple cells?
located along orientation columns which all respond to the same of the orientation which changes depending on the column
(e..g one column responds to a horizontal bar)
What is the difference between the receptive field in the cortex and the receptive field in the retina?
Retina = Small and round
Cortex = Longer
What is a hypercomplex cell?
- When bar turns in to something more complex, hypercomplex cell activates
- If the bar goes out of the receptive field the cells stop responding as the bar starts to activate inhibitory surroundings
What is a complex cell?
- RESPOND TO BARS PRESENTED IN ANY PART OF THE RECEPTIVE FIELD , more based on orientation
- Layers 3,4 and 5
- Input is the simple cells , complex cells receive input from many simple cells with similar orientation
- Bigger receptive field
What is the pattern of what happens in the receptive fields further and further downstream of V1?
- Increase in complexity
- Receptive fields increase in size
Where are face sensitive neurons and how do we know they are face sensitive?
- Temporal lobe
The temporal lobe responds less when you remove specific facial features
How do we use electrodes to study brain stimulation?
- Use electrode in patients that already need them on their brain anyway e.g. epileptic patients
