“Hardware” relating to Cognitive Psychology
- Nervous System
While discussing the nervous system, it is important to discuss the hardware or the nervous system.
Let’s talk about the sense organs we use to receive information i.e. the eyes and the ears
Structure of eyes and the ears imposes limits on our sensory system because there is a limit to what the eyes can see and the ears can hear. There is some range which the eyes cannot see and there Is some range for which the ears cannot hear. Rather, we can say the other way around. The eyes can see only limited and the ears can hear only limited.
In considering the computer-brain analogy, the eye and the camera are analogous.
When we consider computer-brain analogy, we primarily concern ourselves with the eyes and the ears because sound and camera are very much used in computer and are easy to simulate. Taste, smell are not used by computers as yet.
How we process sound?
The information goes to the visual cortex where the information is processed.
*- Delay detectors indicate from where the noise is coming.
It is important to note that the sensory system imposes a limit to our information processing ability.
How sensory information is processed in initial stages?
Information processing (of visual information) is done in the visual cortex.
Let’s look at some classic experiments to see how the information is processed.
Stephen William Kuffler (1913-1980)
Information Processing in Visual cells
How does sensation transform into perception?
*- Kuffler studies ganglion cells and discovered on-off and off-on cells.
Ganglion cells are before brain cells and after optic nerve.
There are two kinds of visual processing:
-On-off cells
-Off-on cells
If the light fell on the center of retina, on-off cells were activated,
If the light fell in the periphery, off-on cells started firing.
Neurons don’t use pistols
Neurons don’t use a pistol to fire. When we say neuron firing, we mean that the neurons release electric impulses to communicate.
By they are activated we mean that neurons start firing electric impulses.
Ganglion Cells
When light falls on the center of retina, the on-off cell fires a lot but the off-on cell did not fire at all.
In the diagram above:
On the left side, there are on-off cells
On the right side, there are off-on cells.
The lines indicate the time
If lots of lines are together they indicate that the neuron is firing many times in one second.
If there is less number of lines means it is firing less.
1. Central light spot
When light was on the center of the retina, the on-off cell fired a lot but the off-on cell did not fire at all.
2. Peripheral light spot
The off-on cell show an opposite reaction as shown by the on-off cell
On-off cell did not fire, there are no lines there
The off-on cell has lot of lines, the off-on cells are activated when there is light in the periphery
3. Central Illumination
If some place is lit, and the illumination is on the center then there is lot of firing in the on-off cell.
4. Surround Illumination
On-off cells are silent
5. Diffused illumination
Both cells are activating but firing very slowly.
The location is determined through on-off cells and off-on cells.
Hubel and Wiesel
- Hubel and Wiesel (1962) constructed a very important experiment in cognitive psychology.
They started their experiment with cats and used their visual cortex.
- Hubel and Wiesel found out that the visual cortex is more complex than on-off cell and off-on cell.
- They discovered:
*- Bar detectors and edge detectors.
*- Edge detectors help us to understand where an object ends and the other starts.
Cats also have the same edge cells which were discovered by Hubel and Wiesel.
David Marr's Work
*- Marr and Hildreth (1980) combined the output of off-on detectors to calculate bars and edges of various widths and orientations.
*- Symbolic descriptions were created.
Computer scientist and AI experts make computer models.
- Marr simulated on-off cells and off-on cells in a computer
- The information was gathered through a program and symbolic descriptions were created.
- Boundaries of objects in the real images present a difficult problem in computer vision.
The computer program was used simulating edge detectors and bar detectors.
This is done because computer vision is an important part of our technology
For example: an airplane running on autopilot
Edge detectors and bar detectors use camera to find out whether there is a bird or cloud or another airplane ahead.
Clouds
For a computer, detecting the image above is a nightmare scenario.
Software Level
What happens when we get all this sensory information?
Sensory Memory
- What happens with the sensory information we receive? All information is held somewhere.
- Cognitive science deals with only 5 senses which are observable and measureable.
-Vision
-Hearing
-Smell
-Taste
-Touch
Most of the work has been focused on vision and hearing because we are limited by technology to conduct experiments on smell, taste and touch.
- Any experimentation that we do in the area of cognitive psychology, we feel that only a limited technology is available to us.
What is Sensory memory?
Sensory memory allows us to take a ‘snapshot’ of our environment and to store this information for a short period. Only information that is transferred to another level of memory will be preserved no more than for two seconds.
Sensory memory holds a short impression of sensory information even when the sensory system does not send any information anymore.
-We keep getting the same sensory information if we are in the same background.
-The sensory memory holds the information for a very brief period of time and that brief period is usually no more than a second.
How we know this?
Visual system experiments on human beings
In the case of cat, electrodes were entered in the brain of the cat and the electric impulses were measured.
*- In human experimentation, the subject is made to sit and is asked to look at a screen, a computer screen normally. A dot is shown on the screen with blank white screen (dot is located in the center) and the subject is asked to focus on the dot.
- Instead of a dot, a set of letters is presented at that fixated point, where the subject is focusing.
- After a very brief period letters (stimuli) are removed.
Sperling's partial report procedure
The same array was presented to the subjects but the subjects were asked to report the letters according to the cue.
(A beep in this case, an auditory cue)
After the array was turned off, a tone was sounded
- High
- Medium
- Low
High tone cue for reporting the top row.
Medium tone cue for reporting the middle row.
Low tone cue for reporting the bottom row.
It is to be noted that using this method:
*- Subjects reported at least 3 out of 4 letters.
*- Because the subjects did not know beforehand which row will be cued, they had to have 3 letters from each row available to them.
The decay in Visual Memory
The number of letters available for the partial-report condition decreases with delay for the cue tone.
All the information that we are getting from our memory is being stored but for a very brief period of time.
References:
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