Sperry Physiological Psychology The Core Studies

Background Cerebral localisation – Looking at the functions of different parts of the brain Corpus callosum – A row of fibres that join the two hemispheres in the brain together. It acts as a “connector” and enables messages from one hemisphere to reach the other Cross wired – Humans are cross wired meaning that the right hemisphere of the brain controls the left side of the body. The left hemisphere thus controls the right. Why the procedure was done - The participants had suffered from severe epilepsy for 10 years that was seeming to be untreatable, so they underwent surgery to sever the corpus callosum so fits could be reduced and the spreading epileptic fits would be reduced to only one hemisphere, not both.

Aim The aim of the study was to test the effects of hemisphere disconnection in humans.

Sample 11 adults At least 1 female All had had their corpus callosum severed to reduce the spread of epileptic seizures.

Method Laboratory experiment/Quasi/Case study’s Repeated measures Snapshot study IV: A severed corpus callosum DV: Ability on the tasks Controls – every person was shown stimuli for a tenth of a second, all were medication free, all completed the same tasks

Procedure the participant had one eye covered and was asked to gaze at a fixed point in the centre of a projector screen. Visual stimuli were back- projected onto the screen, either to the right or left of the screen, at a very high speed – one picture every 1/10th of a second or less. This meant that the eye only had time to process the image in the visual field where it was placed (i.e. if the image was shown to the left visual field there was not time for the participant to move their eye or head so the right visual field might also receive the image). Below the screen was a gap so the participant could reach objects but not see his or her hands. Visual investigations were then conducted which involved flashing one stimuli at a time to one visual field or two stimuli simultaneously to different fields and participants were asked to identify what they saw through speech, writing or drawing. Tactile investigations involved placing an object in one hand or the other, or both hand simultaneously without the participant being able to see what they were holding and then asking them to identify what they had been holding through speech, writing, drawing or manual selection from various objects

Results When participants were presented with an image in one half of their visual field and then presented with the same image in the other half of the visual field they responded as if they had never seen the image before. If the same image was presented in the original visual field the participants were able to recognise the image as one they had seen before Participants were not able to give a description of an image that was presented to the left hand side of the visual field. The image was either not noticed or just appeared as a flash. Although they could respond non-verbally by pointing with their left hand to a matching picture or selecting an object presented among a collection of other pictures and objects. This of course only works with right-handed participants.

Conclusions In split brain patients, perceptions in each hemisphere are independent. Information from one visual field is only passed to one hemisphere and isn’t available to the other Speech is only in the left hemisphere In split brain patients, memory in each hemisphere is independent. Split brain patients are obviously not impaired.

Strengths of the study Both data types are collected which enables more in depth understanding of results and different types of analysis Sperry asked participants how they behaved in real life, asked about real life behaviours therefore conclusions are more reliable and relatable to real life

Weaknesses of the study The severe epilepsy of the participants could have affected their abilities, not just because of the cut cc Does not allow us to generalise to people who have severed corpus callosum’s that do not have epilepsy Low ecological validity – patients with a severed corpus callosum would have both visual fields present some of the patients had experienced more disconnection than others. We also cannot be sure how long each of the participants had experienced ineffective drug therapy which could have been affecting the findings.

Evaluation of the method High control over extraneous variables All participants did all the tasks and all were shown items for a tenth of a second therefore the control of the study is good – reliable Low ecological validity Only a small sample