Biological Flashcards
(19 cards)
B C What was the background?
Visual cortex- part of occiptal lobe, providing a detailed map of the visual image we see.
Neuron-nerve cell
Neuroplasticity- Lasting changed to the brain, change shape or accommodation
Monocular- one eye
Binocular- both eyes
Hubel and Wiesel- in a normal cat neurones of the visual cortex are selective of the orientation of lines and edges in a visual field and the preferred orientations are around the clock.
BC What is the aim?
To investigate the effect on kittens visual development of a restricted visual environment consisting of either vertical or horizontal stripes only in which the animal can move freely.
BC What is the method?
Lab exp, IMD
IV- horizontal/vertical
DV- behavioural/neurophysiological changes
Who was the sample?
Laboratory raised kittens
Houses in darkness until 2 weeks of age
BC Procedure summary?
2 weeks – 5 months
- visual experience of the kittens was manipulated (vertical or horizontal), cylindrical piece of apparatus with a clear glass platform halfway up where the kitten was put. The cylinder was 46 cm in diameter and about 2 metres
high. There was vertical/horizontal high contrast black and white stripes. The kittens spent about 5 hours a day in this apparatus. They wore a wide black collar so that they could not see their own bodies, and this limited their vision to about 130 degrees
5 months- The kittens were then taken for several hours each week to a well-lit room. The psychologists monitored the kittens’ reactions.
7.5 months- Two kittens were anaesthetised, and their neurons were investigated. A normal kitten would have neurons around the clock, i.e. both vertical and horizontal.
Behavioural results?
No visual placing (no stretching their paws when brought close to the table).
No startle response when an object was thrust towards them.
They guided themselves mainly by touch. They were frightened when they reached the edge of the surface they were standing on.
Only the eyes of the kitten brought up in vertical stripes followed a rod held vertically and only the eyes of the kitten reared in horizontal stripes followed the rod if it was held horizontally i.e. behavioural blindness.
Neurophysiological results?
About 75% of cells in both kittens were clearly binocular and in almost every way the responses were like that of a normal kitten.
The distributions of preferred orientation were however totally abnormal, in the way their condition was.
The kittens recovered within 10 hours, unfortunately they always followed objects clumsily and tried to touch things beyond their reach.
BC Main conclusions?
Brain development is determined by functional demands made upon it, rather than pre-programmed genetic factors, i.e. The difference between the kittens suggests that neurons change their preferred orientation according to stimulation received
Ethics evaluaton?
The kittens would have suffered some pain and distress; distress from separation from mother and possible lifelong visual problems;
HOWEVER only 2 were used for invasive neurophysiological testing so there was an attempt to limit suffering + researchers reported that kittens’ didn’t seem upset by the monotony of their surroundings. Quality of research High quality – lots of controls. Certainty of benefit Practical applications could not have been predicted at the time.
Evaluations?
Population validity-
only kittens but likely mammals all share a common organisation of neurones in the visual cortex.
Reliability-
Highly standardised, replicable – check test-retest but only two were tested so the sample is too small for consistent effect. Some quantitative data increasing reliability (neurophysiological findings), however there were some qualitative data too reducing reliability (behavioural).
Internal validity-
High level of control, use of scientific equipment, concurrent validity -> measured behavioural and neurophysiological changes, misleading results = the abnormal brain development resulting from impoverished stimulation. If raised in lab cages, no richness of stimulation associated with living in the natural habitat.
What is the background to Maguire’s study?
Hippocampus is located in the limbic system, each hemisphere has one (2x hippocampus = hippocampi), the hippocampus plays a key role in spatial memory and navigation.
Cognitive mapping is a type of mental representation which helps us to acquire, store and recall information about the locations/environment.
‘The Knowledge’ – Two year course for Black Cab drivers who are required to have a detailed knowledge of the
25,000 streets through central London.
Pixel counting and Voxel Based Morphometry – Techniques used to analyse MRI scans.
M What was the aim?
To investigate whether there was a difference in hippocampal volume between individuals who did, or did not,
have extensive navigational experience.
M What was the method?
Quasi experiment with MPD
IV – London taxi driver or non-taxi driver
DV – Volume of the hippocampi
Correlational analysis
Co-variable 1 – length of taxi driving experience;
Co-variable 2 – grey matter volume of the
hippocampus
M Who was the sample?
16 right-handed male London taxi drivers, varied experience; 1.5-42 years. All were medically, neurologically and psychiatrically healthy.
A comparison group of 50 control participants were chosen from the structural MRI scan database
at the same unit where the taxi drivers were scanned. All right-handed males and healthy; aged
between 32-62. None were taxi drivers.
M Brief procedure?
Data was collected using MRI (Magnetic Resonance Imaging) scans.
Voxel-based morphometry - produces a 3D image measuring the volume of an area by identifying differences in density of grey matter in different areas of the brain.
Pixel counting - in order to calculate hippocampal area, pixels were
counted on photographic ‘slices’ made through the brain using an MRI scan. Pixels were counted for the anterior, posterior and body of the hippocampus.
Correlations conducted.
Blind experimenter.
M What were the main results?
VBM results – Taxi Drivers showed significantly increased grey matter volume in left & right posterior hippocampi. Controls had relatively more grey matter volume in the anterior (R & L) but didn’t reach significance.
Pixel Counting results – no significant differences in total volume. Taxi Drivers had greater volume in the posterior than controls, controls had greater volume in the anterior than the TDs.
Right hippocampi were bigger for both groups.
Correlation results – Positive correlation between length of time as taxi driver and volume of right posterior hippocampi (0.6) and negative correlation between length of time as taxi driver and volume of right anterior hippocampus. The more experienced the driver is, the greater the grey matter volume is in their right posterior hippocampus and the less grey matter volume in their right anterior hippocampus.
Results suggest that there was no overall increase in the volume of grey matter in the hippocampi of taxi drivers – it was redistributed. Therefore we can infer that there are different roles in different parts of the hippocampus: Anterior: This is used when encoding new spatial information, which is more common with people who learn new locations all the time (Non-taxi drivers). Posterior: This is used when previously learned spatial information is used . Right hippocampus: Holds mental maps Left hippocampus: Complements its partner by storing memories i.e. people and events that occur in the taxi drivers’ world (but not necessarily into an existing map).
M Main conclusions?
The distribution of grey matter in the hippocampus changes because the posterior hippocampus stores information about spatial relations in the environment, so its volume increases in response to demand for navigational skill. This is because the correlational data showed that, as taxi drivers developed a better
understanding of routes and locations, improving their cognitive maps over time, the volume of the posterior hippocampus increased.
Ethics evaluation?
Broken- Protection of ps, right to withdraw Difficult to withdraw,
Justifications and/or guidelines adhered to- Informed consent gained for MRI scanning, no deception, confidentiality/privacy, debrief presumed
Evaluation points?
Reliability-
* Highly controlled experiment,
* Quantitative data, i.e. volume of the hippocampus
* Consistency as the same individual assessed all of the images.
Internal validity-
Use of control group – matched on gender, handedness, good psychological and physical health, and age.
No demand characteristics or researched bias due to single blind experimenter. Correlational evidence, so it might be difficult to establish cause and effect (i.e. there might be mediating factors etc.)
