Declarative memory deficits and schizophrenia: problems and prospects

Cognitive deficits are among the most important factors leading to poor functional outcomes in schizophrenia, with deficits in declarative memory among the largest and most robust of these. Thus far, attempts to enhance cognition in schizophrenia have shown only modest success, which underlies increasing efforts to develop effective treatment strategies. This review is divided into three main parts. The first section delineates the nature and extent of the deficits in both patients with schizophrenia and in their adult, non-psychotic relatives. The second part focuses on structural and functional abnormalities in the hippocampus, both in people with schizophrenia and in animal studies that model relevant features of the illness. The third section views problems in declarative memory and hippocampal function from the perspective of elevated rates of common medical disorders in schizophrenia, with a focus on insulin insensitivity/diabetes. The likelihood that poor glucose regulation/availability contribute to declarative memory deficits and hippocampal abnormalities is considered, along with the possibility that schizophrenia and poor glucose regulation share common etiologic elements, and with clinical implications of this perspective for enhancing declarative memory.     

Footprints sticking out of the sand. Part 2: children's Bayesian priors for shape and lighting direction

The shading information in images that depict surfaces of 3-D objects cannot be perceived correctly unless the direction of the illuminating light source is known and, in the absence of this knowledge, perception in adults is consistent with a light-from-above Bayesian prior assumption. In order to investigate if children make use of a similar assumption, 171 children between the ages of 4.6 and 10.8 years were tested with 20 images containing shading information, where the shape depicted in each image could be perceived as either convex or concave. Each child's Bayesian prior probability that light comes from above was estimated, and (assuming that decision-noise is approximately the same in all children) regression analyses revealed a significant increase in this prior probability of 0.034-0.035 per year, and predict a neutral prior (0.5) at 1.6 years for naturalistic picture stimuli and 3.6 years for abstract symbol stimuli. Additionally, each child's prior probability for perceiving shapes as being convex/concave was estimated, and was found to be close to a neutral value of 0.5 for all ages. Together, these results indicate that children have a neutral prior for shape convexity, and that their prior probability for lighting direction gradually shifts towards an adult-like prior value as they grow older. Finally, the status of these one-dimensional priors is discussed in relation to marginal distributions of high-dimensional priors implicit in the statistical structure of the physical word.     

Sizing up information distortion: quantifying its effect on the subjective values of choice options

When choosing between options, people often distort new information in a direction that favors their developing preference. Such information distortion is widespread and robust, but less is known about the magnitude of its effects. In particular, research has not quantified the effects of distortion relative to the values of the choice options. In two experiments, we manipulated participants’ initial preferences in choices between risky three-outcome monetary gambles (win, lose, or neither) by varying the order of five information items (e.g., amount to win, chance of losing). In Experiment 1 (N = 397), the effect of initial information on gambles’ certainty equivalents (subjective values) was mediated by the distortion of later information. The indirect effect on the difference between gambles’ certainty equivalents averaged 27% of the gambles’ mean expected value. In Experiment 2 (N = 791), we increased the difference between gambles on a later information item to overcome the effect of initial information on participants’ choices. The required change averaged 31% of the gambles’ mean expected value. We conclude that the effects of information distortion can be substantial.