Information encoding in short firing rate epochs by single neurons in the primate temporal visual cortex

Abstract

The information available about face identity from the firing rate and from temporal encoding in the spike train of single neurons recorded in the temporal lobe visual cortical areas of rhesus macaques was analysed using principal component and information theory analyses of smoothed spike trains. The neurons analysed had responses selective for faces. The stimulus set consisted of 20 different faces. The first principal component provided by a considerable extent the most information (57%) available in principal components 1–5, with the second adding 18%, the third 16%, and the fourth and fifth adding 9%. For each image, the weighting on the first principal component was highly correlated with the mean firing rate of the neuron to that image. The information available from the firing rate of the neuron was very close to that available in the first principal component. Information theory analysis showed that in short epochs (e.g. 50 msec) the information available from the firing rate can be as high, on average, as 65% of that available from the firing rate calculated over 400 msec, and 38% of that available from principal components 1–3 in the 400-msec period. It was also found that 30% of the information calculated from the first three principal components is available in the firing rates calculated over epochs as short as 20 msec. More information was available near the start of the neuronal response, and the information available from short epochs became less later in the neuronal response. Taken together, these analyses provide evidence that a short period of firing taken close to the start of the neuronal response provides a reasonable proportion of the total information that would be available if a long period of neuronal firing (e.g. 400 msec) were utilized to extract it, even if temporal encoding were used. The implications of these and related findings are that at least for rapid object recognition, each cortical stage provides information to the next in a short period of 20–50 msec, does not rely on temporal encoding, and completes sufficient computation to provide an output to the next stage in this same 20- to 50-msec period.     

Multiple repetition priming of faces: Massed and spaced presentations

Previously viewing a face typically leads to a decrease in the amount of time taken to later identify it (“repetition priming”). Five repetition priming experiments are reported, which investigate whether multiple presentations of a face increase the amount of repetition priming. The results demonstrate similar amounts of priming from massed multiple presentations of the same face or a series of different images (freeze frames selected from a moving clip and presented in sequence), compared with a single unchanging presentation (Experiments 1 and 2). This is true even when different images are presented at prime and test (Experiment 3). However when multiple presentations were presented in a spaced fashion, with one or more intervening items between each repeat, there was significantly more priming in the multiple than single presentation condition (Experiment 4). This was true even when the face was named only once in both the multiple and single spaced conditions (Experiment 5). The results are discussed in relation to face motion.     

Digit ratio (2D:4D), academic performance in computer science and computer-related anxiety

Being able to use information communication technology (ICT) effectively has become an essential element of participation within an increasingly digital culture. However, there are differences in participation within this digital culture. Prenatal testosterone exposure is thought to influence the development of numeric capabilities and relate to levels of anxiety, both of which contribute towards engagement with ICT. This study examined whether an index of prenatal exposure to testosterone, digit ratio (2D:4D), is related to successful involvement within a computer-technology context - performance in a Java programming course. Three studies (N = 73,75,65) identified a consistent negative correlation between 2D:4D digit ratio and attainment (r ≈ −0.2). A fourth study (N = 119) found that 2D:4D digit ratio positively correlated with two indices of computer-related anxieties, as well as anxiety sensitivity (r = 0.32/0.51). These results suggest that males and females who have been exposed to higher levels of testosterone within the womb perform better upon academic assessments of Java-related programming ability within computer science education, and have lower levels of computer-related anxieties outside computer science education. Thus, the 2D:4D index of prenatal testosterone exposure correlated with the two factors that directly impact upon ICT engagement, which is increasingly essential to effectively participate within educational and occupational environments.     

Validation of the Poisoning Severity Score (PSS) in suicidal behavior by self‐poisoning

Intentional self‐poisoning is the leading method of suicidal behavior leading to medical attention worldwide. The medical severity of self‐poisoning events has major treatment, prognostic, and medico‐legal implications, yet measures of severity are limited. The Poisoning Severity Score (PSS) is a widely used scale but validation data are limited, particularly in the study of suicidal behavior per se. The sample was a consecutive series of intentional self‐poisoning patients aged 13 to 65 treated at a large university medical center (n = 673). PSS scores, with a range 0 (none) to 4 (death), were calculated along with other structured clinical data and analyzed in a series of linear regressions adjusted for age and sex. Higher PSS scores were consistently associated with greater medical morbidity and more intensive acute medical treatments, and nearly all effect sizes were large. Results support the validity of the PSS in hospital‐treated self‐poisoning patients.     

Just How Effective are Antidepressant Medications? Results of a Major New Study

The STAR*D (Sequenced Treatment Alternatives to Relieve Depression) project was the largest and most extensive trial of antidepressants ever conducted. The study used state of- the-art methods to treat real patients coming to a hospital or psychiatric clinic for relief from depression. Because the first antidepressant is often ineffective for most patients, a sequence of drug treatments targeting various brain neurochemicals was carefully planned. This article will review the complex treatments and the various outcomes, including the frequency of relapse during twelve months of follow-up care.     

Stochastic transitivity and the unidimensional control of choice

A concurrent-chains paradigm was used to test three models of preference for schedules of reinforcement. Each model assumes choice to be a monotonic function of values on a single dimension (“simple scalability”). For choices involving variable-interval and fixed-interval schedules, this dimension is assumed to be an harmonic average of the interreinforcement intervals; for choices involving fixedinterval and fixed-ratio schedules, the dimension is the time to reinforcement irrespective of response rate; for choices involving different combinations of rate and duration of reinforcement, the dimension is the rate of “reinforcement-time”, or the product of the two parameters. Each model implies a strong form of transitivity (“functional equivalence”), which held for half the subjects (that half exclusively sensitive to the reinforcement variable specified by the model). An alternative unidimensional model which implies a weaker form of transitivity (“weak binary utility model”) was consistent with the preferences of all subjects. This model states that a single factor controls the direction of preferences but not necessarily the exact choice probability, as simple scalability assumes.     

Judged Likelihood of Different Second Crimes: A Function of Judged Similarity

Numerous studies have concluded that the judged probability of conviction for a crime is higher when information concerning a prior conviction is disclosed. This is even more true when the prior and present crimes are the same. This paper examines the argument that the influence of a hypothetical previous conviction on the judgment of predilection toward a hypothetical present crime is a continuous function of the degree of similarity between past and present crimes. The subjects were presented with all possible pairs of 10 crimes, the first being considered as a prior conviction and the second as a presently charged crime. The subjects judged the subjective likelihood that a person convicted of the first crime (C1) would, in fact, he of a mind and inclination to commit the second one (C2). Independent judgments of intercrime, undefined similarity also were obtained. The main experimental findings, as expected, were that the judged probability of C2. given C1, was: (a) greatest when C2 was a repeat of C1; (b) uniquely different for each C1; (c) predicted quite well by degree of intercrime similarity; (d) poorly predicted by crime seriousness values. Thus, the subject appears to make judgments of predilection on the basis of simple representativeness heuristics, which specify that certain crimes will be considered more likely if they are more semantically related to earlier ones. Such a mental device unfortunately would he systematically biased in courtroom settings because judgments of intercrime similarity are not influenced by real-world probabilities.     

Nonmetric grouping: Clusters and cliques

A class of related nonmetric (“monotone invariant”) hierarchical grouping methods is presented. The methods are defined in terms of generalized cliques, based on a systematically varying specification of the degree of indirectness of permitted relationships (i.e., degree of “chaining”). This approach to grouping is shown to provide a useful framework for grouping methods based on ana priori specification of the properties of the desired subsets, and includes a natural generalization for “complete linkage” and “single linkage” clustering, such as the methods of Johnson [1967]. The central feature of the class of methods is a simple iterative matrix operation on the original disparities (“inverse-proximities” or “dissimilarities”) matrix, and one of the methods also constitutes a very efficient single linkage clustering procedure.     

The effects of visual presentation method on single-trial free recall

In two experiments four different conditions of visual presentation were studied with the purpose of furthering our understanding of the role of temporal and spatial factors underlying modality effects in single-trial free recall. Enriching spatial factors in the visual presentation did not produce a higher performance in the recency part of the serial-position curve, and it was therefore concluded that the modality effect could not be due to any visual handicap. A lag distribution measure was suggested and applied to the data to characterize output order (the order of recall) in single-trial free recall. The two experiments carried out used a within-subjects and a between-subjects design, respectively, and illustrate the importance of the methodological difference between these two designs.