Visual temporal integration for threshold,signal detectability,and reaction time measures

A comparison was made of temporal integration for three different response measures in a visual detection task: (1) response frequency, (2) signal detectability as measured for rating ROC curves. (3) simple reaction times (RTs). These measures were obtained on the same trials, to the same stimuli-orange (581 rim) light pulses of 50 min of visual angle fixated foveally and presented to dark-adapted Os in a monocular Maxwellian view. All three response measures showed a period of luminance-duration reciprocity (Bloch’s law), followed by a period of partial integration. The end points of luminance-duration reciprocity (critical duration) and partial integration (utilization time) were shorter for RTs than for the response frequency and signal detectability measures. Neurophysiological.implications of differences in time constants of integration for RT and psychophysical measures are discussed.     

Neuronal assemblies: necessity, signature and detectability

The ease with which highly developed brains can generate representations of a virtually unlimited diversity of perceptual objects indicates that they have developed very efficient mechanisms to analyse and represent relations among incoming signals. Here, we propose that two complementary strategies are applied to cope with these combinatorial problems. First, elementary relations are represented by the tuned responses of individual neurons that acquire their specific response properties (feature selectivity) through appropriate convergence of input connections in hierarchically structured feed-forward architectures. Second, complex relations that cannot be represented economically by the responses of individual neurons are represented by assemblies of cells that are generated by dynamic association of individual, featureselective cells. The signature identifying the responses of an assembly as components of a coherent code is thought to be the synchronicity of the respective discharges. The compatibility of this hypothesis is examined in the context of recent data on the dynamics of synchronization phenomena, the dependence of synchronization on central states and the relations between the synchronization behaviour of neurons and perception.     

Gustatory,salivary, and oral thermal responses to solutions of sodium chloride at four temperatures

Using eight highly trained Ss, sensitivity to near threshold levels of NaCl was significantly greater at solution temperatures of 22° and 37°C than at 0° or 55°C. Perceived intensity increased linearly with concentration (0.04%–0.64% NaCl) at all four solution temperatures, with the two lower considered slightly more intense than the two higher temperatures. Biomodal distributions were obtained for hedonic judgments at all temperatures, with three Ss showing greater liking and five Ss showing greater disliking of increasing concentrations. Parotid salivary flow was inversely related to the taste sensitivity, i.e., significantly lower flow rates were obtained for the intermediate than for the hot or cold solutions, independent of salt content. When solution temperature was O°C, the minimum temperature of the oral cavity was 9°–20°C; when solution temperature was 55°C, the maximum temperature of the oral cavity was46°–49°C.     

Discrimination thresholds for haptic perception of volume, surface area, and weight

The present study investigated the human ability to discriminate the size of 3-D objects by touch. Experiment 1 measured the just noticeable differences (JNDs) for three tasks: (1) discrimination of volume without availability of weight information, (2) discrimination of volume with weight information available, and (3) discrimination of surface area. Stimuli consisted of spheres, cubes, and tetrahedrons. For all shapes, two reference sizes were used (3.5 and 12 cm(3)). No significant effect of task on the discriminability of objects was found, but the effects of shape and size were significant, as well as the interaction between these two factors. Post hoc analysis revealed that for the small reference, the Weber fractions for the tetrahedron were significantly larger than the fractions for the cube and the sphere. In Experiment 2, the JNDs for haptic perception of weight were measured for the same objects as those used in Experiment 1. The shape of objects had no significant effect on the Weber fractions for weight, but the Weber fractions for the small stimuli were larger than the fractions for the large stimuli. Surprisingly, a comparison between the two experiments showed that the Weber fractions for weight were significantly larger than the fractions for volume with availability of weight information. Taken together, the results reveal that volume and weight information are not effectively combined in discrimination tasks. This study provides detailed insight into the accuracy of the haptic system in discriminating objects' size. This substantial set of data satisfies the need for more fundamental knowledge on haptic size perception, necessary for a greater understanding of the perception of related properties, as well as of more general perceptual processes.