Biomedical subjects

C H John

Publications and source records attributed to C H John.

3 recordsLinked to original sources

PubMed1997

The effect of self-referent material on the reasoning of people with delusions.

People with delusions have been shown to have both generalized (Huq, Garety & Hemsley, 1988) and content-specific biases in reasoning (Bentall, 1994). Our concern here was whether the hastiness that has been found when people with delusions reason on relatively abstract tasks would be present on a more realistic task. A second concern was whether reasoning with salient or emotional material would increase the hastiness bias in people with delusions. Two versions of a probabilistic reasoning task were used to study the data gathering of people with delusions. The first version employed realistic but emotionally neutral material. People with delusions requested less evidence before making a decision than psychiatric and normal comparison groups. Therefore, the hastiness found previously with abstract materials was seen to generalize to a more realistic task. In the second version participants were required to reason with material that had an emotional content and may have been regarded as being personally meaningful. In this condition all groups reduced the amount of evidence requested before making a decision.

Adult↗

PubMed1997

Normal and abnormal reasoning in people with delusions.

People who experience delusions have been found to request less information prior to making a decision than control participants on tasks that are unrelated to the theme of the delusion (Huq, Garety & Hemsley, 1988). Two studies investigated whether people with delusions have an absolute deficit in reasoning or a more specific data-gathering bias. In Expt 1, 12 people with delusions, 12 people with depression and 12 normal controls were shown the results of spinning a supposedly biased coin. The evidence provided varied in the number of heads to tails. In normal controls a high ratio of head to tails produces a high estimate that the coin is biased. In this experiment, where the evidence gathered was predetermined by the experimenter, all groups of participants were shown to reason in a similar way. Experiment 2 tested whether a difference would exist between the groups in conditions where participants were free to determine the amount of evidence seen, in contrast to when all of them viewed the same evidence. Two jars of beads in opposite but equal ratios (e.g. 85:15, 15:85) were shown to 15 people with delusions, 15 with depression and 15 normal controls. On the basis of beads being drawn one at a time, it was the participants' task to determine which jar they came from. When free to decide when they wished, people with delusions decided on the basis of less evidence than the other groups. However, as in Expt 1, the group with delusions did not differ when made to view the same amount of beads as other participants. Therefore, people with delusions have a data-gathering bias rather than a difficulty in employing the data in reasoning. This "jump to conclusions' bias generalized to a less discriminable ratio of beads (60:40), and was not a consequence of impulsiveness or memory deficit.

Adolescent↗

PubMed1992

Gestalt perception in schizophrenia.

An experiment is described which investigates perceptual processing in schizophrenia. It examines the extent to which subjects employ top-down and bottom-up processing strategies in the interpretation of tachistoscopically presented images. The findings support the hypothesis that schizophrenic subjects do not benefit as controls do from the use of automatic, top-down processing of deeper level stimuli containing semantic information. However, it illustrates that, given sufficient processing time (up to 1000 ms), schizophrenics are able to compensate for this deficit by employing a bottom-up strategy requiring longer processing time. The findings suggest that the specific processing abnormalities in schizophrenia are amenable to detailed measurement, and some suggestions are made for further investigation.

Adult↗