Laboratory experiments look for cause-and-effect relationships by controlling as much as possible, implementing an artificial task in an artificial and controlled environment. Everything is kept as identical as possible, except for the independent variable (IV) which is manipulated in order to see the effect that it has on the dependent variable (DV). A hypothesis is generated from a theory and then tested. The theory is then amended or confirmed according to the results of the experiment.
Loftus and Palmer’s laboratory experiment is a well know one into eyewitness testimony (EWT). Loftus has carried out many experiments into EWT and has highlights how it is not always reliable as there are certain factors which can affect a jury’s perception of an account of witness testimony. She carried out experiments, usually by showing students films and then asking them leading or misleading questions.
The misinformation effect refers to what happens when a witness is given the wrong information and is used to see if they will incorporate it into their witness testimony, or if it will go unnoticed. Loftus noticed that it affects what participants will report to have seen and it forms the second part of the experiment that Loftus and Palmer conducted when they asked about broken glass. By leaving a gap between viewing the film and asking questions it leaves people more open to the misinformation effect.
People can also accept false childhood memories as their own even if they didn’t happen. Loftus used experiments to demonstrate this, planting non-traumatic memories of being lost in a shopping centre, which never occurred but the ‘memories’ were still remembered by 29% of participants (pps) and 25% of pps remembered the memories at a later date.
Laboratory experiments have been the main way of investigating witness effectiveness since the 1970s because everything except the IV can be controlled which means that we can establish a cause-and-effect relationship.
They are replicable because of their strong controls. They are very detailed and someone could repeat it exactly. They are of repeated by the researcher and other people to establish the reliability. This gives them more value in the world of psychological research.
Laboratory experiments usually lack validity because of their strong controls. For example, Loftus used students who had to watch a film and this is not like a ‘real’ situation, unlike asking someone questions after they have witnessed a crime. Because of this there are also potentially demand characteristics.
The pps should give consent, or there will be either presumptive or retrospective consent. There may be some deception but this can be counteracted with a good debrief. If the researcher is planting false memories they need to be careful not to cause any distress or psychological harm.