Postreinforcement signal processing

Postreinforcement signal processing by rats was demonstrated in six experiments that used a discrete-trials choice procedure. Experiment 1 assessed the extent to which rats are able to transfer knowledge about associations between postreinforcement signal durations and choice responses to conditions where a particular signal duration preceded the opportunity to make a choice response. In Experiment 2 the generality of the transfer effect was demonstrated by using both signal duration and signal modality as relevant stimulus attributes for the postreinforcement signals. The role of the relative durations of the reinforcement-signal gap and the intertrial interval was investigated in Experiment 3. In order to assess the effects of within-trial and between-trial signal relations on the acquisition of a temporal discrimination, both pre-and postreinforcement signals were presented on each trial in Experiments 4 and 5. The effects of pre- and postreinforcement signal relations on the steady-state performance of a temporal bisection task across three different signal ranges were studied in Experiment 6. The conclusion is that rats readily process various stimulus attributes of postreinforcement signals and that relations between postreinforcement signals, choice responses, and prereinforcement signals are major determinants of choice behavior.     

Low-frequency filtering and the processing of local-global stimuli

The role of low-spatial-frequency information in the processing of global stimuli made up of local elements was examined. After selective removal of low spatial frequencies two major changes occurred in the pattern of results. First, response times to global stimuli were significantly slower and the usual speed advantage of global over local processing was lost. Second, when processing local features the usual decrease in response speed when the local and global letters are not the same (consistency effect) was not obtained. These effects could not be explained by changes in error rate, by contrast variation resulting from the process of filtering, or by loss of visual sensitivity due to greater eccentricity of global images.     

A psycho-ethological approach to social signal processing

The emerging field of social signal processing can benefit from a theoretical framework to guide future research activities. The present article aims at drawing attention to two areas of research that devoted considerable efforts to the understanding of social behaviour: ethology and social psychology. With a long tradition in the study of animal signals, ethology and evolutionary biology have developed theoretical concepts to account for the functional significance of signalling. For example, the consideration of divergent selective pressures responsible for the evolution of signalling and social cognition emphasized the importance of two classes of indicators: informative cues and communicative signals. Social psychology, on the other hand, investigates emotional expression and interpersonal relationships, with a focus on the mechanisms underlying the production and interpretation of social signals and cues. Based on the theoretical considerations developed in these two fields, we propose a model that integrates the processing of perceivable individual features (social signals and cues) with contextual information, and we suggest that output of computer-based processing systems should be derived in terms of functional significance rather than in terms of absolute conceptual meaning.     

A psycho-ethological approach to social signal processing

The emerging field of social signal processing can benefit from a theoretical framework to guide future research activities. The present article aims at drawing attention to two areas of research that devoted considerable efforts to the understanding of social behaviour: ethology and social psychology. With a long tradition in the study of animal signals, ethology and evolutionary biology have developed theoretical concepts to account for the functional significance of signalling. For example, the consideration of divergent selective pressures responsible for the evolution of signalling and social cognition emphasized the importance of two classes of indicators: informative cues and communicative signals. Social psychology, on the other hand, investigates emotional expression and interpersonal relationships, with a focus on the mechanisms underlying the production and interpretation of social signals and cues. Based on the theoretical considerations developed in these two fields, we propose a model that integrates the processing of perceivable individual features (social signals and cues) with contextual information, and we suggest that output of computer-based processing systems should be derived in terms of functional significance rather than in terms of absolute conceptual meaning.     

Interactions of signal and background variables in visual processing

Three variables which determine the opportunities for signal-noise confusions, display size (D), number of redundant signals per display (N), and number of alternative signals (A) were studied in relation to nature of the noise elements, confusable or nonconfusable with signals. Data were obtained in a forced-choice visual detection situation, the displays being linear arrays of letters on a CRT screen. For all three performance measures used, frequency of correct detections and correct and error latencies, strong interactions were obtained between all of the other variables and signal-noise confusability. The functions obtained, together with other data bearing on the role of confusions and on spatial relations among characters within the display, suggest a model whose initial phase is a parallel feature extraction process involving inhibitory relations among input channels.     

Digital filtering in EEG/ERP analysis: Some technical and empirical comparisons

A general approach to time domain digital filtering is described, and examples of some filters used in EEG/ERP research are presented. Simulations are reported that evaluate the impact of the relative length of the filter weight series and the signal cycle to be filtered, the span and real-time density of the filter weights, and slow drift across the epoch being filtered. Results indicate that some filters commonly used in the EEG/ERP literature are inadequate. Frequency domain digital filtering is also briefly discussed. The fast Hartley transform, a fast but relatively unknown computational method for frequency domain filtering of ERP/EEG data, is introduced and compared with time domain filtering. Some practical recommendations are provided.     

The effect of spatial-frequency filtering on the visual processing of global structure

In three experiments we measured reaction times (RTs) and error rates in identifying the global structure of spatially filtered stimuli whose spatial-frequency content was selected by means of three types of 2-D isotropic filters (Butterworth of order 2, Butterworth of order 10, and a filters with total or partial Gaussian spectral profile). In each experiment, low-pass (LP), bandpass (BP), and high-pass (HP) filtered stimuli, with nine centre or cut-off spatial frequencies, were used. Irrespective of the type of filter, the experimental results showed that: (a) RTs to stimuli with low spatial frequencies were shorter than those to stimuli with medium or high spatial frequencies, (b) RTs to LP filtered stimuli were nearly constant, but they increased in a nonmonotonic way with the filter centre spatial frequency in BP filtered stimuli and with the filter cut-off frequency in HP filtered stimuli, and (c) the identification of the global pattern occurred with all visible stimuli used, including BP and HP images without low spatial frequencies. To remove the possible influence of the energy, a fourth experiment was conducted with Gaussian filtered stimuli of equal contrast power (c(rms) = 0.065). Similar results to those described above were found for stimuli with spatial-frequency content higher than 2 cycles deg(-1). A model of isotropic first-order visual channels collecting the stimulus spectral energy in all orientations explains the RT data. A subsequent second-order nonlinear amplitude demodulation process, applied to the output of the most energetic first-order channel, could explain the perception of global structure of each spatially filtered stimulus, including images lacking low spatial frequencies.     

A novel signal processing approach to auditory phantom perception

Psychonomic Bulletin & Review - The ear and brain interact in an orchestrated manner to create sensations of phantom tones that are audible to listeners despite lacking physical presence in...     

Design and operation of an EEG-based brain-computer interface with digital signal processing technology

We are developing an electroencephalographic (EEG)-based brain-computer interface (BCI) system that could provide an alternative communication channel for those who are totally paralyzed or have other severe motor impairments. The essential features of this system are as follows: (1) EEG analysis in real time, (2) real-time conversion of that analysis into device control, and (3) appropriate adaptation to the EEG of each user. Digital signal processing technology provides the speed and flexibility needed to satisfy these requirements. It also supports evaluation of alternative analysis and control algorithms, and thereby facilitates further BCI development.     

Perceptual degradation due to signal alteration: implications for auditory pattern processing.

When a passage is alternately presented to the right and left ears over headphones, perceptual processing is disrupted under certain conditions: When the signal alternation rate is approximately 3-4 cps, intelligibility is greatly reduced. Experiment 1 demonstrated that contrary to previous theorizing, the effect is not mediated by the disruption of syllabic units. Experiment 2 explored the generality of the perceptual degradation by testing perception of simple piano melodies. The basic effect holds for these complex auditory patterns. The final experiment tested a source-effect explanation of the phenomenon by using 3 signal locations (right, middle, and left) rather than 2. The degree of disruption depends on the likelihood that sounds are assigned to different sources. Together, the experiments help to account for the strikingly selective breakdown in perceptual processing and speak to the issues of perceptual units, domain specificity, and auditory source assignment.     

Conflict-induced perceptual filtering

In a variety of conflict paradigms, target and distractor stimuli are defined in terms of perceptual features. Interference evoked by distractor stimuli tends to be reduced when the ratio of congruent to incongruent trials is decreased, suggesting conflict-induced perceptual filtering (i.e., adjusting the processing weights assigned to stimuli associated with the target and with the distractor features). In search of evidence for such a mechanism, we administered a flanker task, in which targets and distractors were defined in terms of stimulus location (Experiment 1) or color (Experiment 2). The efficiency of processing stimuli associated with target and distractor features was assessed in intermixed trials of a visual search task, in which a target had to be detected irrespective of these features. In both experiments search times were shorter for stimuli associated with the target feature than with the distractor feature of the flanker task. This effect was increased under conditions of a reduced congruent/incongruent ratio, thereby providing evidence for conflict-dependent perceptual filtering.