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At least 19 recordsLinked to original sources
PubMedDate not supplied

Can we resolve contradictions between process dissociation models?

Wainwright and Reingold (1996) presented equations for various versions of the process dissociation procedure that has been used to separate conscious and unconscious memory process. In the present reply it is suggested that these equations, though helpful, may not capture some of the key theoretical possibilities that could help to resolve apparent contradictions and paradoxes in the empirical literature. Specifically, there could be an independence of processes that might be estimated to a sufficient degree of accuracy for some theoretical purposes despite a violation of the assumption of stochastic independence.

Humans↗
PubMed1996

Neuromodulation of transduction and signal processing in the end organs of taste.

Chemical synapses transmit gustatory signals from taste receptor cells to sensory afferent axons. Chemical (and electrical) synapses also provide a lateral pathway for cells within the taste bud to communicate. Lateral synaptic pathways may represent some form of signal processing in the peripheral end organs of taste. Efferent synaptic input may also regulate sensory transduction in taste buds. To date, the synaptic neurotransmitter(s) or neuromodulator(s) released at chemical synapses in taste buds have not been identified unambiguously. This paper summarizes the attempts that have been made over the past 40 years to identify the neuroactive substances acting at taste bud synapses. We review the four traditional criteria for identifying chemical transmitters elsewhere in the nervous system-localization, uptake/degradation, release and physiological actions- and apply these criteria to neuroactive substances in taste buds. The most complete evidence to date implicates serotonin as a neuromodulator of taste transduction in the end organs. However, studies also suggest that adrenergic, cholinergic and peptidergic neurotransmission may be involved in taste buds.

Animals↗
PubMed1995

Infants require low-frequency energy to hear the pitch of the missing fundamental.

The present experiment assessed 7- to 8-month-old infants' perception of pitch for harmonic tonal complexes containing either low- or high-frequency energy. In a visually reinforced, operant head turn procedure, infants first learned to discriminate two harmonic tonal complexes based on missing fundamental frequencies of 160 and 200 Hz. After learning this basic task, infants were presented with spectrally varying harmonic tonal complexes that contained either resolvable, low-frequency energy, or unresolvable, high-frequency energy. Infants learned to categorize the low-frequency signals according to the pitches of their missing fundamental frequencies but failed to categorize the high-frequency signals. These results suggest that infants require low-frequency, resolvable energy to hear the pitch of the missing fundamental.

Child Development↗
PubMed1996

Processing visual evoked potentials based on matched filtering of single trial responses.

Physiological signals recorded after presentation of a stimulus can be considered as the sum of an evoked sensory response and uncorrelated noise corresponding to the spontaneous neural background activity. In case of low signal-to-noise ratio, the sensory signal is estimated by averaging a large number of single trial records sampled under the same experimental conditions. The averaging technique, however, is inappropriate for displaying trial-to-trial variations that may occur during a recording session. A method based on matched filtering was developed for processing single visual evoked potentials (VEPs). To illustrate the performance of this method, a set of VEPs for grating patches of 8 different contrasts (including 0) was evaluated. The VEPs were subjected to signal detection analysis by computing for each contrast similarity indices between the single trial records and the averaged response used as a template. The signals were analysed in terms of probability density distributions, expressing the goodness of fit between template and each single waveform.

Cluster Analysis↗
PubMed1995

Expectancy for change and adaptation to a new signal probability.

An experiment showed that the higher the 18 observers' expectancy for change in signal probability (without knowing the future probability), the more successful the adaptation to a new probabilistic environment in terms of shift in response criterion.

Adaptation, Psychological↗
PubMed1995

Process dissociation, single-process theories, and recognition memory.

According to the assumptions of L. L. Jacoby's (1991) process dissociation method, performance in recognition memory is determined by the combination of an unconscious familiarity process and a conscious intentional recollection process. The process dissociation method is used to produce estimates of the contributions of the 2 components to recognition performance. This article investigates whether the method provides the correct estimates of components if performance actually depends on only a single process or on 2 processes different from those assumed by the method. The SAM model (G. Gillund & R. M. Shiffrin, 1984) was used to produce simulated data based on a single process. Variants of SAM with 2 processes and R. C. Atkinson and J. F. Juola's (1973) 2-process model were used to produce data based on 2 processes.

Cognition↗
PubMed1994

Categorization response time with multidimensional stimuli.

Categorization response time (RT) was examined in three separate experiments, in each of which exemplars varied on two physical dimensions. Three different types of stimuli were used: (1) horizontal and vertical line segments of varying length that were joined at an upper left corner, (2) rectangles of varying width and height, and (3) circles or semicircles of varying size with a radial arm of varying orientation. No evidence was found that stimulus familiarity or the category prototypes played any special role in determining categorization RT. Instead, RT decreased with distance from the stimulus to the categorization decision bound.

Decision Making↗
PubMed1996

The degradation of distance discrimination in big brown bats (Eptesicus fuscus) caused by different interference signals.

The ability of two big brown bats (Eptesicus fuscus) to discriminate the distance to an electronically synthesized "phantom" target by echolocation was tested in the presence of interfering signals presented slightly before the target echo. Interfering signals were chosen to have differing degrees of similarity to the typical echolocation emission used by the bat in this task (which was the signal used to create the phantom target), and we predicted that the degree of disruption of ranging would be proportional to the similarity of the interference to the target echo. This prediction was not confirmed; rather, all interference signals not identical to the target echo increased the threshold to about twice that found with no interference. When the interference was identical to the target echo, the threshold increased to about 4 times that with no interference. When each bat was presented with phantom target "echoes" appropriate for the other bat, its range discrimination threshold increased about ten fold, and in this case the degree of interference of different signals was related to their similarity to the target echo, not to their similarity to the bat's "normal" signal. We suggest that Eptesicus may suppress interference by a more sophisticated strategy than simple linear matched filtering.

Animals↗
PubMed1996

Meridional anisotropy in the discrimination of parallel and perpendicular lines--effect of body tilt.

It is well documented that orientation discrimination is poorer for stimuli oriented obliquely than for those that are vertical or horizontal. Buchanan-Smith and Heeley recently reported that in the absence of a spatial reference this anisotropy follows gravitational rather than retinal coordinates, suggesting a high-level basis for the anisotropy in unreferenced orientation discrimination tasks. In the present study, unlike the previous one, the effects of body tilt on orientation discrimination have been examined in the presence of explicit simultaneous spatial references. The thresholds for discrimination of two parallel or two perpendicular lines were estimated for the retinally principal and oblique orientations, with the body either erect or tilted 45 degrees with respect to gravity. In agreement with previous studies, meridional anisotropy for both parallelism and perpendicularity discrimination was found when observers were seated upright. When the observer's body was tilted, the anisotropy for the parallelism task was mapped to retinal and not to gravitational coordinates after compensating for countertorsion. Initially, the anisotropy for the perpendicularity task was not mapped to retinal coordinates, but after extensive practice for both the erect and the tilted body conditions it eventually followed retinal coordinates. The results reported here suggest that contrary to orientation discrimination without a spatial reference, the ultimate limits for both parallelism and perpendicularity discriminations are located at orientation-sensitive cortical neurons. However, the effect of perceptual learning in the perpendicularity task suggests that the internal frame of reference (gravity cues and body axis) also plays an important role.

Analysis of Variance↗
PubMed1996

The optimum decision rules for the oddity task.

This paper presents the optimum decision rule for an m-interval oddity task in which m-1 intervals contain the same signal and one is different or odd. The optimum decision rule depends on the degree of correlation among observations. The present approach unifies the different strategies that occur with "roved" or "fixed" experiments (Macmillan & Creelman, 1991, p. 147). It is shown that the commonly used decision rule for an m-interval oddity task corresponds to the special case of highly correlated observations. However, as is also true for the same-different paradigm, there exists a different optimum decision rule when the observations are independent. The relation between the probability of a correct response and d' is derived for the three-interval oddity task. Tables are presented of this relation for the three-, four-, and five-interval oddity task. Finally, an experimental method is proposed that allows one to determine the decision rule used by the observer in an oddity experiment.

Decision Making↗
PubMed1996

High-order behaviour in learning gate networks with lateral inhibition.

In this work we present a neural network model incorporating activity-dependent presynaptic facilitation with multidimensional inputs. The processing unit used is based on a slightly simplified version of the Learning Gate Model proposed by Ciaccia et al. (1992). The network topology integrates a well-known biological neural circuit with a lateral inhibition connection subnet. By means of simulation experiments, we show that the proposed networks exhibit basic and high-order features of associative learning. In particular, overshadowing and blocking are reproduced in the presence of both noise-free and noisy inputs. The role of noise in the development of high-order learning capabilities is also discussed.

Animals↗
PubMed1995

Conflict, receiver bias and the evolution of signal form.

In a model, conflicts of interest between communicating individuals are shown to have an important influence on the cost and form of signals that evolve. Two types of conflict are considered: competition between senders to obtain a response from the receiver, and conflict between the sender and the receiver. The receiver system is modelled as an artificial neural network whose 'resistance' to signals is represented as a motivational factor that varies independently of the signal. Biases in the receiver system act as the selective force on signals, causing them to become more costly and conspicuous as the intensity of conflict increases. There is some evidence that competition between senders and sender-receiver conflict may have qualitatively different outcomes. We give examples of some situations to which the model might be applied and point out some predictions that could be tested empirically.

Animal Communication↗
PubMed1994

Skilled speechreading: a single-case study.

In a case study the cognitive characteristics of a skilled visual speechreader (SJ) was examined and compared to a group. SJ is a 56 year old woman, skilled in visual speechreading. She differs from most of the 119 individuals in the control group, as she uses a particular speechreading strategy in which she attempts to repeat overtly each spoken word as soon as it has been uttered, and to summarize and fill in missing pieces of information whenever it is possible (e.g., during pauses) during the conversation. SJ outperformed the control group on three types of tasks; a reading span task, performance in the asymptote level in the serial position curve, and verbal inference-making. SJ's results were discussed with respect to (a) how they related to the general case (i.e., models based on group-data) and to (b) her speechreading strategy. From a clinical perspective it was suggested that it might be possible to practice the strategy as such, but any possible improvement is dependent on the individual's capability to process information in this way.

Cognition↗
PubMed1995

Relation between stimulus discriminability and response bias in a delayed conditional discrimination task in the rat.

The present study investigated whether changes in response bias (log b) affect discriminability (log d) in a delayed conditional discrimination (DCD) task. Eight rats were trained on an DCD task and response bias was manipulated by changing the reinforcement ratio (RR) for correct responding on the two response alternatives. Three findings emerged. First, changes in RR produced changes in log b and the magnitude of these changes was related to the value of the RR. Second, log d was affected by changing RRs. Third, the effect of changes in RR on log b was larger after longer delays. These results suggest that log d and log b are not independent and it is concluded that changes in response bias (log b) may affect the discriminability measure log d. This implies that changes in log d may be mediated by changes in response bias and it is therefore recommended that log d and log b values are both reported when investigating effects of, for example, pharmacological manipulations on DCD performance.

Animals↗
PubMed1995

On the nature of streaks in signal detection.

Human performance in the domain of signal detection is analyzed with respect to the formation of streaks. Streakiness was found to be a general property of auditory and visual discrimination in the sense that correct and incorrect responses have a positive sequential dependency. Success tends to follow success and failure tends to follow failure. Level of streakiness was discovered to be a function of the attentional demand required by the discrimination. Discriminations that make the least demand on attentional resources produce the highest level of streakiness. Monte-Carlo simulations of the observed data sequences suggest that streaky performance is a residue of wave-like variations in perceptual and attentional resources.

Attention↗
PubMed1996

Effects of stimulus source and intensity on covert orientation to auditory stimuli.

Normal subjects showed costs and benefits of informative auditory spatial cues with auditory targets in RT tasks when stimulus intensity was low, or when the stimuli were presented monaurally through headphones. These findings imply that attention to auditory stimuli, like attention to visual or tactile stimuli, can be shifted spatially in detection tasks, and that covert orienting to auditory stimuli occurs in conditions favoring the intention to orient the head to a sound source. According to this view, orienting of attention to auditory stimuli, as well as to visual and tactile stimuli, is linked functionally to mechanisms controlling overt orienting movements that increase stimulus identification.

Adolescent↗
PubMedDate not supplied

Changes in secreted salivary sodium are sufficient to alter salt taste sensitivity: use of signal detection measures with continuous monitoring of the oral environment.

A signal detection measure of NaCl taste sensitivity was developed with continuous monitoring of the Na+ concentration of the oral environment. Taste sensitivity was reduced when saliva was stimulated by chewing to secrete with elevated Na+ levels. Monitoring of the oral environment for Na+ allowed a computation of physical signal strengths for NaCl and water stimuli; changes in these strengths, brought about by variations in secreted salivary sodium, furnish an explanation for alterations in NaCl taste sensitivity.

Adult↗