Identifying neural correlates of consciousness: the state space approach

This article sketches an idealized strategy for the identification of neural correlates of consciousness. The proposed strategy is based on a state space approach originating from the analysis of dynamical systems. The article then focuses on one constituent of consciousness, phenomenal awareness. Several rudimentary requirements for the identification of neural correlates of phenomenal awareness are suggested. These requirements are related to empirical data on selective attention, on completely intrinsic selection and on globally unconscious states. As an example, neuroscientific findings on synchronized gamma activity are categorized according to these requirements.     

Septal infusions of glucose or pyruvate,but not fructose,produce avoidance deficits when co-infused with the GABA agonist muscimol

Although glucose typically enhances memory or reverses memory deficits, glucose can also produce memory deficits when co-infused with the gamma-aminobutyric acid (GABA) agonist muscimol into the medial septum (Parent & Gold, 1997; Parent, Laurey, Wilkniss, & Gold, 1997). To date the mechanisms underlying the memory-impairing interaction between GABA and glucose remain unknown. Here we investigate whether this effect is the result of hyperosmolar conditions or may involve glucose metabolism. Male Sprague-Dawley rats were given one-trial inhibitory avoidance training after receiving septal infusions of vehicle (phosphate-buffered saline, 0.5 microl), the GABA(A) agonist muscimol (3 nmol), glucose (16.5, 33, or 66 nmol), fructose (33 nmol), pyruvate (33 nmol), or a solution containing muscimol combined with glucose, fructose, or pyruvate. Retention performance was tested 48 h later. Infusions of glucose, pyruvate, fructose, or muscimol alone did not affect retention performance. However, co-infusions of all doses of glucose (16.5, 33, or 66 nmol) or the glycolytic end product pyruvate with muscimol impaired retention performance. Co-infusions of fructose with muscimol did not affect retention performance. These results suggest that the memory-impairing interaction between glucose and muscimol does not result from hyperosmolar conditions, because equiosmolar concentrations of fructose do not mimic the effects of glucose and the memory deficits do not vary as a function of glucose concentration. The finding that pyruvate mimicked the effects of glucose and impaired memory when combined with muscimol suggests that glucose metabolism may be involved in the memory-impairing interaction between glucose and GABA(A) receptors in the medial septum.     

Speeded recognition of ungrammaticality: Double violations

A model of sentence comprehension postulating that Subject-Verb-Object relations are specified prior to Noun-Adjective relations received support from a study of the speed at which sentences with various kinds of violations could be rejected. Compatible with the sequential model was the finding that Noun-Verb and Adjective-Noun double violations did not result in shorter RTs than Noun-Verb single violations — even though sentences with double violations were judged to be less acceptable.     

The logical and empirical bases of conservation judgements

It is argued that conservation judgements are based on a particular combination of logical necessity and empirical belief. The empirical belief is that a given transformation will not alter a particular quantity (Elkind's conservation of identity). The logical aspect is a transitive deductive argument containing an initial equivalence of two quantities and the conservation of identity belief as premises which lead to the conclusion of maintained equivalence (Elkind's conservation of equivalence). In two experiments, it is shown that conservation of identity beliefs can be manipulated in subjects who have long since developed the capacity for transitive deductive inference. Untrained 10 year olds were unaware of how sublimation acts to alter certain quantities over particular transformations of shape. And untrained adults incorrectly believed that both the area and perimeter of a closed figure would be conserved over transformations which elongated the figure. Both groups of subjects could be trained in the correct conservation of identity beliefs and this affected their conservation of equivalence judgements in predicted ways. It is suggested that the locical aspect of conservation is developmentally stable and that the empirical aspect varies widely across problems and individuals because of its dependence on relevant experience.     

Extradimensional transfer in the easy-to-hard effect

In three experiments analyzing determinants of the easy-to-hard effect, pigeons acquired a hard discrimination after training on other problems. Intradimensional pretraining resulted in immediate transfer to the hard discrimination. Extradimensional pretraining consistently did not produce immediate transfer but did facilitate learning rate. In Experiment 1, the compounding of cues from an easy extradimentsional discrimination with those from the hard discrimination resulted in the former overshadowing the latter. When different types of extradimensional discriminations were introduced in Experiments 2 and 3, the degree of transfer was not proportional to the similarity in incidental background cues across problems. The findings indicate that in the easy-to-hard effect: (a) intra- and extradimensional mechanisms jointly contribute to the development of stimulus control, (b) intradimensional transfer is more consistent with the gradient-interaction model than the selective attention model, and (c) extradimensional transfer is better accounted for by the construct of general attentiveness rather than by the neutralization of background cues.     

Duration of failure,causal attributions for failure,and subsequent reactions

Subjects were given a preliminary problem solving task of either short or long duration, and were told that they could shorten the duration of aversive noise bursts by correctly solving the problems. They were then given false feedback that they had done either well or poorly on the problems. Two groups of failing subjects were given information designed to lead them to attribute failure to either lack of ability or a difficult task. Two additional groups received “success” or “failure” feedback without any attributional cues. Failure-induced stress was reported to be greater under short duration conditions than under long duration conditions, and increased to the extent that subjects were led to believe they were personally responsible for failure. Following the preliminary failure period, task performance in the same situation and task performance and persistence in a different situation were assessed. In each case, performance and persistence decreased (a) following short-duration failure when subjects were led to attribute failure to a difficult task, and (b) following long-duration failure when subjects were led to attribute failure to lack of ability. These results are discussed within a framework that emphasizes the role of casual attributions in mediating the effects of failure.     

Effect of thought-stopping on thoughts,mood and corrugator EMG in depressed patients

The immediate effects of thought-stopping applied to depressive thoughts were compared to those of a control procedure in a group of depressed psychiatric day-patients. Thought-stopping had only a weak effect on average in reducing the frequency of depressive thoughts, and no significant effects on depressed mood or corrugator EMG. A small significant effect on anxious mood appeared related to non-specific factors. The results raise the possibility that thought-stopping may have little specific effect in reducing the frequency of unwanted thoughts. Corrugator EMG was significantly related to the frequency of spontaneously occurring depressive thoughts both between and within subjects.     

Feature selection and classification: A developmental study

Two hundred and thirteen children between the ages of 4 and 16 sorted 30 complex objects freely into groups. These were either schematic faces, schematic imaginary animals, or histoform patterns and were constructed from 9 independently and continuously varying features, each with 10 levels. The three sets were equivalent in terms of underlying numerical structure. A new method of analysis of the groups formed yielded the following direct measures of subjective organization in the sorting of each child: the number of features used in sorting, the accuracy of sorting, and the number of independent dimensions of classification. Both the material and the analysis of sorting were devised on the assumption that only some of the component features of complex objects are used for classification, while others are ignored. Sorting performance differed markedly both with age and with different types of material. The improvement in sorting ability with age, except for the youngest children, could be attributed to an increase in the number of features used rather than an improvement in the accuracy of use. In contrast, the poor sorting of histoform patterns as opposed to faces and animals was due to a low level of sorting accuracy. The basic results on the development of classification confirmed previous studies, and hence suggest that it is valid to consider feature selection as a basic component of classification.     

Blocking of a taste aversion by prior pairings of exteroceptive stimuli with illness

Although rats preferentially associate gustatory stimuli with illness, this does not imply that other types of stimuli cannot be associated with illness. In Experiment 1, rats consuming tap water in a distinctive environment prior to illness subsequently suppressed ingestion in that environment, whereas rats poisoned or injected with saline 10 hr later did not. It was also found that rats poisoned after drinking saccharin in the environment paired with illness developed weaker saccharin aversions than identically trained rats which drank saccharin in a different location. In Experiment 2, degrading the correlation between injection-related cues and illness by interpolating saline injections between LiCl preexposures attenuated the decremental effects of illness preexposure. The strength of the exteroceptive cue-illness associations observed in these studies suggests that theories based on evolutionary arguments are not the most appropriate frame of reference for analyzing stimulus selection in poison-induced avoidance.