Biomedical subjects

Lawrence M Ward

Publications and source records attributed to Lawrence M Ward.

9 recordsLinked to original sources

PubMed2004

Stochastic resonance and sensory information processing: a tutorial and review of application.

OBJECTIVE: To review the stochastic resonance phenomena observed in sensory systems and to describe how a random process ('noise') added to a subthreshold stimulus can enhance sensory information processing and perception. RESULTS: Nonlinear systems need a threshold, subthreshold information bearing stimulus and 'noise' for stochastic resonance phenomena to occur. These three ingredients are ubiquitous in nature and man-made systems, which accounts for the observation of stochastic resonance in fields and conditions ranging from physics and engineering to biology and medicine. The stochastic resonance paradigm is compatible with single-neuron models or synaptic and channels properties and applies to neuronal assemblies activated by sensory inputs and perceptual processes as well. Here we review a few of the landmark experiments (including psychophysics, electrophysiology, fMRI, human vision, hearing and tactile functions, animal behavior, single/multiunit activity recordings). Models and experiments show a peculiar consistency with known neuronal and brain physiology. A number of naturally occurring 'noise' sources in the brain (e.g. synaptic transmission, channel gating, ion concentrations, membrane conductance) possibly accounting for stochastic resonance phenomena are also reviewed. Evidence is given suggesting a possible role of stochastic resonance in brain function, including detection of weak signals, synchronization and coherence among neuronal assemblies, phase resetting, 'carrier' signals, animal avoidance and feeding behaviors. CONCLUSIONS: Stochastic resonance is a ubiquitous and conspicuous phenomenon compatible with neural models and theories of brain function. The available evidence suggests cautious interpretation, but justifies research and should encourage neuroscientists and clinical neurophysiologists to explore stochastic resonance in biology and medical science.

Animals↗

PubMed2004

Inhibition of return from stimulus to response.

In a standard inhibition-of-return (IOR) paradigm using a manual key-press response, we examined the effect of IOR both on the amplitude of early sensory event-related brain potential (ERP) components and on the motor-related lateralized readiness potential (LRP). IOR was associated with a delay of premotor processes (target-locked LRP latency) and reduced sensory ERP activity. No effect of IOR was found on motor processes (response-locked LRP latency). Thus, IOR must arise at least in part from changes in perceptual processes, and, at least when measured with manual key presses, IOR does not arise from inhibition of motor processes. These results are consistent with the results of attention-orienting studies and provide support for an inhibition-of-attention explanation for IOR.

Evoked Potentials, Visual↗

PubMed2003

Behavioral stochastic resonance within the human brain.

We provide the first evidence that stochastic resonance within the human brain can enhance behavioral responses to weak sensory inputs. We asked subjects to adjust handgrip force to a slowly changing, subthreshold gray level signal presented to their right eye. Behavioral responses were optimized by presenting randomly changing gray levels separately to the left eye. The results indicate that observed behavioral stochastic resonance was mediated by neural activity within the human brain where the information from both eyes converges.

Adult↗

PubMed2003

Event-related potential evidence for attentional inhibition of return in audition.

Orienting attention to a spatial location facilitates responding to a subsequent target at that location, but inhibits the response if attention is oriented away from that location before the target appears there. This inhibitory effect of attention re-orienting, called inhibition of return (IOR), occurs in vision, hearing, touch, and cross-modally, and has been well studied behaviorally. However, little is known about its underlying neural mechanism(s). We report a study of the neural mechanism of auditory IOR using event-related potentials (ERPs). Auditory IOR was associated with elimination, but not reversal, of the Nd1 difference wave. Previous research indicates that the Nd1 represents an enhanced neural response to attended sounds. Also, auditory IOR was associated with a delay in the latency of the peak of the N1 component of the ERP at parietal sites. These effects are consistent with the accounts if inhibition of attention return that have been proposed for IOR, but are somewhat different from effects found in analogous ERP studies of visual IOR.

Adult↗

PubMed2003

Synchronous neural oscillations and cognitive processes.

The central problem for cognitive neuroscience is to describe how cognitive processes arise from brain processes. This review summarizes the recent evidence that synchronous neural oscillations reveal much about the origin and nature of cognitive processes such as memory, attention and consciousness. Memory processes are most closely related to theta and gamma rhythms, whereas attention seems closely associated with alpha and gamma rhythms. Conscious awareness may arise from synchronous neural oscillations occurring globally throughout the brain rather than from the locally synchronous oscillations that occur when a sensory area encodes a stimulus. These associations between the dynamics of the brain and cognitive processes indicate progress towards a unified theory of brain and cognition.

Journal Article↗

PubMed2003

Regional variation and changes with ageing in vibrotactile sensitivity in the human footsole.

Recently there has been indirect evidence suggesting that age-related elevation in footsole vibration detection may be associated with balance and gait dysfunction. As a first step in investigating this dysfunction, the current study determined by how much plantar vibration sensation decreases as a function of age, and if change is dependent on frequency and location of vibration application. Vibration thresholds were assessed at 4 frequencies (25-400 Hz), at 55 locations, and in young and older participants. Results showed there were 3 regions of sensitivity on the footsole: the ball/medial arch, the lateral border of the foot and heel, and the toes. Thresholds for fast-adapting type I receptor (FAI)-mediated frequencies were age invariant; however, thresholds for fast-adapting type II receptor (FAII)-mediated frequencies increased with age. These changes may be one of many factors contributing to age-related changes in gait.

Adult↗

PubMed2003

Goal-driven modulation of stimulus-driven attentional capture in multiple-cue displays.

Six location-cuing experiments were conducted to examine the goal-driven control of attentional capture in multiple-cue displays. In most of the experiments, the cue display consisted of the simultaneous presentation of a red direct cue that was highly predictive of the target location (the unique cue) and three gray direct cues (the standard cues) that were not predictive of the location. The results indicated that although target responses were faster at all cued locations relative to uncued locations, they were significantly faster at the unique-cue location than at the standard-cue locations. Other results suggest that the faster responses produced by direct cues may be associated with two different components: an attention-related component that can be modulated by goal-driven factors and a nonattentional component that occurs in parallel at multiple direct-cue locations and is minimally affected by the same goal-driven factors.

Attention↗

PubMed2002

Stochastic resonance in psychophysics and in animal behavior.

A recent analysis of the energy detector model in sensory psychophysics concluded that stochastic resonance does not occur in a measure of signal detectability ( d'), but can occur in a percent-correct measure of performance as an epiphenomenon of nonoptimal criterion placement [Tougaard (2000) Biol Cybern 83: 471-480]. When generalized to signal detection in sensory systems in general, this conclusion is a serious challenge to the idea that stochastic resonance could play a significant role in sensory processing in humans and other animals. It also seems to be inconsistent with recent demonstrations of stochastic resonance in sensory systems of both nonhuman animals and humans using measures of system performance such as signal-to-noise ratio of power spectral densities and percent-correct detections in a two-interval forced-choice paradigm, both closely related to d'. In this paper we address this apparent dilemma by discussing several models of how stochastic resonance can arise in signal detection systems, including especially those that implement a "soft threshold" at the input transform stage. One example involves redefining d' for energy increments in terms of parameters of the spike-count distribution of FitzHugh-Nagumo neurons. Another involves a Poisson spike generator that receives an exponentially transformed noisy periodic signal. In this case it can be shown that the signal-to-noise ratio of the power spectral density at the signal frequency, which exhibits stochastic resonance, is proportional to d'. Finally, a variant of d' is shown to exhibit stochastic resonance when calculated directly from the distributions of power spectral densities at the signal frequency resulting from transformation of noise alone and a noisy signal by a sufficiently steep nonlinear response function. All of these examples, and others from the literature, imply that stochastic resonance is more than an epiphenomenon, although significant limitations to the extent to which adding noise can aid detection do exist.

Animals↗

PubMed2002

Auditory frequency-based inhibition differs from spatial IOR.

Uninformative auditory frequency cues have a facilitatory effect on reaction time and accuracy of detection and intensity discrimination of target tones for cue-target intervals of up to 3 sec (Green & McKeown, 2001; Ward, 1997). Under some conditions, however, this facilitatory effect can reverse to an inhibitory effect at cue-target intervals longer than 450 msec (Mondor, Breau, & Milliken, 1998). Thepresent work demonstrates that such inhibitory effects are not found in target-target experiments (Experiment 1) or in cue-target experiments requiring a go-no-go discrimination of the target (Experiment 2), whereas they do appear in the paradigm used by Mondor et al. (1998, Experiment 3), albeit unaffected by the similarity of cue and target. Thus, the frequency-based inhibitory effects sometimes found in auditory cuing tasks can be distinguished empirically from those characterizing spatial inhibition of return (IOR), which are found in both target-target and go-no-go cue-target paradigms. The present work and functional and neurophysiological arguments all support the position that different mechanisms underlie spatial IOR and the inhibitory effects sometimes found in auditory frequency processing.

Auditory Perception↗