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PubMed2005

Feature representations and analytic/nonanalytic processing.

Lee Brooks' original formulation of instance theory embedded the notion of an instance within the larger conception of a distinction between analytic and nonanalytic processing. Brooks has recently argued that features can be represented either in terms of their specific feature appearance, or in terms of the abstract information some particular instantiation embodies. This work reviews some recent studies that link reliance on different types of feature representations to different decision-making processes, and to different patterns of categorization behaviour. This in turn complicates the analytic/nonanalytic distinction, suggesting a more precise reformulation.

Decision Making↗
PubMed2006

How MT cells analyze the motion of visual patterns.

Neurons in area MT (V5) are selective for the direction of visual motion. In addition, many are selective for the motion of complex patterns independent of the orientation of their components, a behavior not seen in earlier visual areas. We show that the responses of MT cells can be captured by a linear-nonlinear model that operates not on the visual stimulus, but on the afferent responses of a population of nonlinear V1 cells. We fit this cascade model to responses of individual MT neurons and show that it robustly predicts the separately measured responses to gratings and plaids. The model captures the full range of pattern motion selectivity found in MT. Cells that signal pattern motion are distinguished by having convergent excitatory input from V1 cells with a wide range of preferred directions, strong motion opponent suppression and a tuned normalization that may reflect suppressive input from the surround of V1 cells.

Algorithms↗
PubMed2005

The Hermann grid illusion revisited.

The Hermann grid illusion consists of smudges perceived at the intersections of a white grid presented on a black background. In 1960 the effect was first explained by a theory advanced by Baumgartner suggesting the illusory effect is due to differences in the discharge characteristics of retinal ganglion cells when their receptive fields fall along the intersections versus when they fall along non-intersecting regions of the grid. Since then, others have claimed that this theory might not be adequate, suggesting that a model based on cortical mechanisms is necessary [Lingelbach et al, 1985 Perception 14(1) A7; Spillmann, 1994 Perception 23 691 708; Geier et al, 2004 Perception 33 Supplement, 53; Westheimer, 2004 Vision Research 44 2457 2465]. We present in this paper the following evidence to show that the retinal ganglion cell theory is untenable: (i) varying the makeup of the grid in a manner that does not materially affect the putative differential responses of the ganglion cells can reduce or eliminate the illusory effect; (ii) varying the grid such as to affect the putative differential responses of the ganglion cells does not eliminate the illusory effect; and (iii) the actual spatial layout of the retinal ganglion cell receptive fields is other than that assumed by the theory. To account for the Hermann grid illusion we propose an alternative theory according to which the illusory effect is brought about by the manner in which S1 type simple cells (as defined by Schiller et al, 1976 Journal of Neurophysiology 39 1320-1333) in primary visual cortex respond to the grid. This theory adequately handles many of the facts delineated in this paper.

Contrast Sensitivity↗
PubMed2005

Early age-related cognitive impairment in mice lacking cannabinoid CB1 receptors.

The molecular mechanisms contributing to the normal age-related decline of cognitive functions or to pathological learning and memory impairment are largely unknown. We demonstrate here that young mice (6-7 weeks) with a genetic deletion of the cannabinoid CB1 receptor performed as well as WT mice, or often better, in a number of learning and memory paradigms, including animal models of skill-learning, partner recognition, and operant conditioning. In contrast, the performance of mature mice (3-5 months) lacking CB1 receptors was much worse than that of age-matched WT animals. In most tests, these mice performed at the same level as old animals (14-17 months), suggesting that the decline in cognitive functions is accelerated in the absence of CB1 receptors. This rapid decline in CB1-deficient animals is accompanied by a loss of neurons in the CA1 and CA3 regions of the hippocampus.

Aging↗
PubMed2005

Auditory orientation in crickets: pattern recognition controls reactive steering.

Many groups of insects are specialists in exploiting sensory cues to locate food resources or conspecifics. To achieve orientation, bees and ants analyze the polarization pattern of the sky, male moths orient along the females' odor plume, and cicadas, grasshoppers, and crickets use acoustic signals to locate singing conspecifics. In comparison with olfactory and visual orientation, where learning is involved, auditory processing underlying orientation in insects appears to be more hardwired and genetically determined. In each of these examples, however, orientation requires a recognition process identifying the crucial sensory pattern to interact with a localization process directing the animal's locomotor activity. Here, we characterize this interaction. Using a sensitive trackball system, we show that, during cricket auditory behavior, the recognition process that is tuned toward the species-specific song pattern controls the amplitude of auditory evoked steering responses. Females perform small reactive steering movements toward any sound patterns. Hearing the male's calling song increases the gain of auditory steering within 2-5 s, and the animals even steer toward nonattractive sound patterns inserted into the species-specific pattern. This gain control mechanism in the auditory-to-motor pathway allows crickets to pursue species-specific sound patterns temporarily corrupted by environmental factors and may reflect the organization of recognition and localization networks in insects.

Acoustic Stimulation↗
PubMed2005

Tactile form and location processing in the human brain.

To elucidate the neural basis of the recognition of tactile form and location, we used functional MRI while subjects discriminated gratings delivered to the fingertip of either the right or left hand. Subjects were required to selectively attend to either grating orientation or grating location under identical stimulus conditions. Independent of the hand that was stimulated, grating orientation discrimination selectively activated the left intraparietal sulcus, whereas grating location discrimination selectively activated the right temporoparietal junction. Hence, hemispheric dominance appears to be an organizing principle for cortical processing of tactile form and location.

Adult↗
PubMed2005

Teaching face-name associations to survivors of traumatic brain injury: a sequential treatment approach.

Recalling names in real-world contexts is often difficult for survivors of traumatic brain injury despite successful completion of face-name association training programmes. This small number study utilized a sequential treatment approach in which a traditional training programme preceded real-world training. The traditional training component was identical across programmes: one-on-one intervention using visual imagery and photographs to assist in mastery of face-name associations. The real-world training component compared the effectiveness of three cueing strategies--name restating, phonemic cueing and visual imagery--and was conducted by the actual to-be-named people. Results revealed improved name learning and use by the participants regardless of cueing strategy. After treatment targeting six names, four of five participants consistently used two or more names spontaneously and consistently knew three or more names in response to questioning. In addition to documenting the effectiveness of real-world treatment paradigms, the findings call into question the necessity for preliminary traditional intervention.

Adult↗
PubMedDate not supplied

Age differences in tactile pattern recognition at the fingertip.

Young (21-26 years, n=20) and old (55-86 years, n=25) participants were tested for their ability to recognize raised letters (6-mm high, 1-mm relief) by touch. Spatial resolution thresholds were also measured with grating domes to derive an index of the degree of afferent innervation at the fingertip. Letter recognition in the young group was very consistent and highly accurate (mean, 86% correct), contrasting with the performance of the old group, which was more variable and comparatively low in accuracy (mean, 53% correct). In both groups, spatial resolution thresholds accounted for a substantial portion of the variance in the performance, suggesting a strong link between age-dependent variations in tactile innervation and recognition accuracy. The patterns of errors in the old group showed that an inability to encode internal elements specific to certain letters was at the source of most confusion among letters. Whether this inability reflected only deficient peripheral encoding mechanisms or some other alterations at the central level is discussed.

Adult↗
PubMedDate not supplied

Multiple views of the response of an ensemble of spectro-temporal features support concurrent classification of utterance, prosody, sex and speaker identity.

Models of auditory processing, particularly of speech, face many difficulties. These difficulties include variability among speakers, variability in speech rate and robustness to moderate distortions such as time compression. In contrast to the 'invariance of percept' (across different speakers, of different sexes, using different intonation, and so on) is the observation that we are sensitive to the identity, sex and intonation of the speaker. In previous work we have reported that a model based on ensembles of spectro-temporal feature detectors, derived from onset sensitive pre-processing of a limited class of stimuli, preserves significant information about the stimulus class. We have also shown that this is robust with respect to the exact choice of feature set, moderate time compression in the stimulus and speaker variation. Here we extend these results to show a) that by using a classifier based on a network of spiking neurons with spike-driven plasticity, the output of the ensemble constitutes an effective rate coding representation of complex sounds; and b) that the same set of spectro-temporal features concurrently preserve information about a range of qualitatively different classes into which the stimulus might fall. We show that it is possible for multiple views of the same pattern of responses to generate different percepts. This is consistent with suggestions that multiple parallel processes exist within the auditory 'what' pathway with attentional modulation enhancing the task-relevant classification type. We also show that the responses of the ensemble are sparse in the sense that a small number of features respond for each stimulus type. This has implications for the ensembles' ability to generalise, and to respond differentially to a wide variety of stimulus classes.

Acoustic Stimulation↗
PubMed2006

Measuring sensory processing patterns of older Chinese people: psychometric validation of the adult sensory profile.

The Adult Sensory Profile (ASP) evaluates the sensory experiences of adults in the categories of auditory, visual, taste/smell, touch, movement, and activity level. It generates four sensory processing patterns including low registration, sensation seeking, sensory sensitivity, and sensation avoiding. This study examined the psychometric properties of the Chinese version of ASP (ASP-CV) for older Hong Kong Chinese adults. Ninety-six participants with normal cognitive functioning and 33 participants with dementia were recruited. All participants were involved in the investigation of internal consistency and construct validity. One sub-sample from each group was selected for test-retest reliability and inter-rater reliability respectively. The ASP-CV demonstrated excellent inter-rater reliability and test-retest reliability (r = 0.91-0.99 and 0.76-0.88 respectively), and satisfactory internal consistency (alpha = 0.58-0.72). The construct validity of ASP-CV was supported by the known-groups method, in which participants with dementia differed significantly from their healthy counterparts in the patterns of 'low registration' (F(1, 127) = 9.69, p = 0.002), 'sensory sensitivity' (F(1, 127) = 4.63, p = 0.033), and 'sensation avoiding' (F(1, 127) = 15.87, p < 0.001). In conclusion, ASP-CV is reliable and valid to measure sensory processing functions of older Hong Kong Chinese people. Further studies are suggested to examine the factor structure of and the equivalence of self-report and proxy report of ASP-CV.

Activities of Daily Living↗
PubMed2004

Qualitative analysis of WMS-III Logical Memory and Visual Reproduction in temporal lobe epilepsy.

Clinical observation of performance on the Logical Memory (LM) and Visual Reproduction (VR) subtests from the WMS-III has revealed some variability in retention rates across stories and figures. This paper examined the degree to which this variability occurs in lateralized temporal lobe epilepsy (TLE) in comparison to a matched group from the WMS-III standardization sample, and explored whether analysis of qualitative aspects of LM and VR performance yield additional lateralizing information in TLE. Analysis of LM and VR scaled scores revealed differences between the TLE groups for LM, but not VR scores. All subjects benefited from repetition of LM Story B, with greater improvement in story retention in the Left versus Right TLE group. Variability in VR recall across figures was seen in all groups, with a bimodal distribution of retention rates for each figure and a sizable percentage of each group completely forgetting two or more figures. These results suggest that more careful analysis of individual LM story performance may be useful in some patients with TLE, whereas variability in VR retention across figures is common and should not be over interpreted.

Adult↗
PubMed2005

Tunable retina encoders for retina implants: why and how.

Current research towards retina implants for partial restoration of vision in blind humans with retinal degenerative dysfunctions focuses on implant and stimulation experiments and technologies. In contrast, our approach takes the availability of an epiretinal multi-electrode neural interface for granted and studies the conditions for successful joint information processing of both retinal prosthesis and brain. Our proposed learning retina encoder (RE) includes information processing modules to simulate the complex mapping operation of parts of the 5-layered neural retina and to provide an iterative, perception-based dialog between RE and human subject. Alternative information processing technologies in the learning RE are being described, which allow an individual optimization of the RE mapping operation by means of iterative tuning with learning algorithms in a dialog between implant wearing subject and RE. The primate visual system is modeled by a retina module (RM) composed of spatio-temporal (ST) filters and a central visual system module (VM). RM performs a mapping 1 of an optical pattern P1 in the physical domain onto a retinal output vector R1(t) in a neural domain, whereas VM performs a mapping 2 of R1(t) in a neural domain onto a visual percept P2 in the perceptual domain. Retinal ganglion cell properties represent non-invertible ST filters in RE, which generate ambiguous output signals. VM generates visual percepts only if the corresponding R1(t) is properly encoded, contains sufficient information, and can be disambiguated. Based on the learning RE and the proposed visual system model, a novel retina encoder (RE*) is proposed, which considers both ambiguity removal and miniature eye movements during fixation. Our simulation results suggest that VM requires miniature eye movements under control of the visual system to retrieve unambiguous patterns P2 corresponding to P1. For retina implant applications, RE* can be tuned to generate optimal ganglion cell codes for epiretinal stimulation.

Action Potentials↗
PubMed2005

Haptic feature extraction.

This study examined the process by which the shape of a haptically explored object is synthesized from the geometric characteristics of simpler constituent elements, such as arcs and ellipses. Subjects traced the outlines of virtual objects by means of whole arm movements. Each object consisted of the union of a large central ellipse and two smaller circles, extending upward and outward from the top left and right sides of the base. The sizes of the two circles and the eccentricity of the elliptical base were varied. After exploring the object's contour in the absence of vision, subjects reproduced the sensed shape by means of freehand drawing. Speed and force were modulated during the exploratory phase in a manner that suggested that subjects reacted to rather than predicted changes in curvature. Also, subjects typically devoted more time to exploring the part of the contour encompassing the two smaller circles. During drawing, individual features of the explored shape were reproduced with varying degrees of fidelity. Aspects related to the size and location of the smaller circles were reproduced better than was the eccentricity of the ellipse forming the base. Since subjects spent proportionally less time exploring the base, these results suggest that subjects selectively focused attention to regions of high spatial contrast and that the exploratory strategy introduced distortions in the haptically sensed shapes.

Form Perception↗
PubMed2007

Plastic phase-locking and magnetic mismatch response to auditory deviants in temporal lobe epilepsy.

The magnetic equivalent (MMNm) of mismatch negativity may reflect auditory discrimination and sensory memory. To study whether temporal lobe epilepsy (TLE) affects automatic central auditory-change processing, we recorded magnetoencephalographic (MEG) responses to standard and duration-deviant sounds in 12 TLE patients and 12 age-matched controls, and repeated MEG measurement in 8 patients 6-30 months following epilepsy surgery and in 6 controls 3-8 months after their first measurement. We compared the MMNm between patients and controls, and also evaluated intertrial phase coherences as indexed by phase-locking factors (PLF) using wavelet-based analyses. We observed longer MMNm latencies for patients than for controls. Dipole modeling and minimum-current estimates together showed bi-frontotemporal sources for MMNm. The phase locking across trials was dominant at the 4- to 14-Hz band, and the main difference in PLF between deviant- and standard-evoked responses occurred in the time frame of 150-250 ms after stimulus onset. Notably, in the 5 patients who became seizure free after removal of right temporal epileptic focus, the phase-locking phenomena resulting from deviant stimuli were enhanced, and even more distributed in the frontotemporal regions. We conclude that mesial TLE might affect auditory-change detection, and a successful surgery causes a possible plastic change in phase locking of deviant-evoked signals.

Acoustic Stimulation↗
PubMed2006

Giving learners the best of both worlds: do clinical teachers need to guard against teaching pattern recognition to novices?

PURPOSE: There has been much debate in the medical education literature regarding the extent to which feature-driven and nonanalytic (similarity-based) reasoning strategies define expertise, but the relative value of teaching these strategies, together or in isolation, remains uncertain. The purpose of this study was to compare the diagnostic accuracy achieved upon receiving instruction to use each strategy in isolation to that of a combined approach. METHOD: In 2003-04, 48 undergraduate psychology students from McMaster University in Ontario, Canada, were taught to diagnose ten cardiac disorders (including normal) via electrocardiogram (ECG) presentation. Twelve students were instructed to carefully identify all features present before assigning a diagnosis (feature first). Twelve were given the same instruction with notice that some test ECGs had been seen during training (implicit combined). Twelve were simply instructed to trust familiarity and diagnose based on this impression (similarity-based). Finally, 12 students were given feature first and similarity-based instructions in combination (explicit combined). RESULTS: No difference in diagnostic accuracy was observed between the groups given the feature first (42%) and first impression (41%) instructions (p > .4), but the groups instructed to use both strategies (explicitly or implicitly) performed significantly better (56% and 53%, respectively; p < .01). CONCLUSIONS: The results support an additive model of clinical reasoning in which instructions to be feature oriented and to trust similarity improve performance in novice diagnosticians.

Adult↗
PubMedDate not supplied

Human central auditory plasticity associated with tone sequence learning.

We investigated learning-related changes in amplitude, scalp topography, and source localization of the mismatch negativity (MMN), a neurophysiological response correlated with auditory discrimination ability. Participants (n = 32) underwent two EEG recordings while they watched silent films and ignored auditory stimuli. Stimuli were a standard (probability = 85%) and two deviant (probability = 7.5% each for high [HD] and low [LD]) eight-tone sequences that differed in the frequency of one tone. Between recordings, subjects practiced discriminating the HD or LD from the standard for 6 min. The amplitude of the LD MMN increased significantly across recordings in both groups, whereas the amplitude of the HD MMN did not. The LD was easier to discriminate than was the HD. Thus, practicing either discrimination increased the MMN for the easier discrimination. Learning and changes in the LD MMN amplitude were highly correlated. Source localizations of event-related potentials (ERPs) to all stimuli revealed bilateral sources in superior temporal regions. Compared with the standard ERP, the LD ERP revealed a stronger source in the left superior temporal region in both recordings, whereas the right-sided source became stronger after learning. Consistent with prior studies of auditory plasticity in animals and humans, tone sequence learning induced rapid neurophysiological plasticity in the human central auditory system. The results also suggest that there is asymmetric hemispheric involvement in tone sequence discrimination learning and that discrimination difficulty influences the time course of learning-related neurophysiological changes.

Acoustic Stimulation↗
PubMed2004

Demonstration of nondeclarative sequence learning in mice: development of an animal analog of the human serial reaction time task.

In this paper, we demonstrate nondeclarative sequence learning in mice using an animal analog of the human serial reaction time task (SRT) that uses a within-group comparison of behavior in response to a repeating sequence versus a random sequence. Ten female B6CBA mice performed eleven 96-trial sessions containing 24 repetitions of a 4-trial sequence. During the 12th session, the repeating sequence was replaced with the random sequence halfway through the session. Reaction time (RT) to respond to an illuminated nose-poke was recorded, and performance was compared at the halfway point in each session to test for any change in behavior. For learning effect, RTs decreased over the no-switch repeating-sequence sessions. For interference effect, behavior did not change appreciably at the halfway point during the last repeating-sequence session. However, RTs deteriorated significantly after the switch from repeating to random sequences halfway through session 12. The mice demonstrated a robust interference effect when switched from repeating to random sequences. This pattern of behavior in humans performing the SRT is interpreted as evidence of nondeclarative sequence learning. The similarity between the human and mouse SRTs will enable more direct comparisons of mouse-human nondeclarative memory behavior and will provide a useful behavioral end-point in mouse-models of basal ganglia dysfunction.

Analysis of Variance↗