Biomedical subjects

F van der Velde

Publications and source records attributed to F van der Velde.

6 recordsLinked to original sources

PubMed1997

On the statistical independence of color and shape in object identification.

M. J. Nissen (1985) showed that color and shape are processed independently. M. A. Monheit and J. C. Johnston (1994) argued that dependence of color and shape in these experiments was reduced due to random guessing. They conducted 4 experiments in which they attempted to reduce the effect of random guessing. A strong dependence of color and shape reports was observed. In this article the effects that random guessing can have on statistical (in)dependence are analyzed. The authors argue that Monheit and Johnston's analysis is incorrect and inconsistent with the data they report and that random guessing can be the cause of statistical dependence of color and shape reports.

Attention↗

PubMed1994

Evaluation of motility enrichment on modified semisolid Rappaport-Vassiliadis medium (MSRV) and automated conductance in combination with Rambach agar for Salmonella detection in environmental samples of a milk powder factory.

The efficacy of motility enrichment on modified semisolid Rappaport-Vassiliadis medium (MSRV) and an automated conductance method for the detection of Salmonella in environmental samples was evaluated. Two hundred and ten environmental samples from unrestricted areas of a milk powder factory, 49 of which were artificially contaminated with Salmonella infantis, were examined. From exactly 100 samples Salmonella could be isolated. With the conventional (ISO-DIS 6579) method a 100% score was obtained, whereas the MSRV method gave 82 positive results. The conductance method permitted the detection of Salmonella in only 66 samples. The use of Rambach agar improved isolation efficiency of Salmonella from enrichment broths.

Animals↗

PubMed1993

Is the brain an effective Turing machine or a finite-state machine?

A theorem presented by Hornik, Stinchcombe, and White (1989) suggested the possibility that connectionist networks could be effectively Turing machines. Levelt (1990) argued that the theorem of Hornik et al. only implies that networks are finite-state machines and are therefore not capable of generating the very unlimited productivity of symbol systems. Yet it can be argued that all real machines, including the brain, are finite-state machines. If so, no real machine actually possesses the very unlimited productivity of symbol systems. So any model of actual behaviour should capture the limitations on productivity inherent in the situation. Thus connectionist networks can be valuable models in psychology, precisely because they are finite-state machines.

Brain↗

PubMed1993

An element in the visual field is just a conjunction of attributes: a critique of Bundesen (1991)

Nissen (1985) presented results showing that in partial-report experiments, selection by location was different from selection by color or by shape. Bundesen (1991) presented a reinterpretation of these results, claiming that they can also be explained by a model in which location selection is treated on a par with selection by color or by shape. We will show that the analysis given by Bundesen is based on a special relation between an "element" in the visual field and its location, which in fact reduces the expressions given by Bundesen to those given by Nissen. Furthermore, we will show that in Bundesen's theory, it is assumed that in the process of perceptual categorization an element in the visual field can be referred to without the use of one of its attributes. This assumption is untenable from a theoretical point of view. In all, the results presented by Nissen can still be regarded as evidence for the difference between selection by location and selection by color or by shape.

Attention↗

PubMed1989

Context-dependent migrations in visual word perception.

In the present study we investigate the effect of context--that is, a prime--on migration errors. Migration errors, or migrations, are caused by perceptual interactions between two words in a visual display, such as line-lace. After postcuing, subjects sometimes report lane or lice, instead of the requested word line. This phenomenon has been demonstrated by previous studies. In the experiments reported here, we replicate this phenomenon. We also find that more migrations of the lane type occur (compared with lice type), when the display line-lace is preceded by a prime related to lane (but not to lice). This shows that higher order word knowledge, in the form of semantic relations between words, influences the migration phenomenon. Further, we show that the number of migration errors are not a result of only a summation of activation from the letters in the display. The method we developed to isolate context-dependent migrations also gives valuable information about the effect of contextual information on word perception.

Attention↗

PubMedDate not supplied

From artificial neural networks to spiking neuron populations and back again.

In this paper, we investigate the relation between Artificial Neural Networks (ANNs) and networks of populations of spiking neurons. The activity of an artificial neuron is usually interpreted as the firing rate of a neuron or neuron population. Using a model of the visual cortex, we will show that this interpretation runs into serious difficulties. We propose to interpret the activity of an artificial neuron as the steady state of a cross-inhibitory circuit, in which one population codes for 'positive' artificial neuron activity and another for 'negative' activity. We will show that with this interpretation it is possible, under certain circumstances, to transform conventional ANNs (e.g. trained with 'back-propagation') into biologically plausible networks of spiking populations. However, in general, the use of biologically motivated spike response functions introduces artificial neurons that behave differently from the ones used in the classical ANN paradigm.

Action Potentials↗