Dominant Cue Research Articles

The neural representation of interaural time differences in gerbils is transformed from midbrain to cortex.

Interaural time differences (ITDs) are the dominant cue for the localization of low-frequency sounds. While much is known about the processing of ITDs in the auditory brainstem and midbrain, there have been relatively few studies of ITD processing in auditory cortex. In this study, we compared the neural representation of ITDs in the inferior colliculus (IC) and primary auditory cortex (A1) of gerbils. Our IC results were largely consistent with previous studies, with most cells responding maximally to ITDs that correspond to the contralateral edge of the physiological range. In A1, however, we found that preferred ITDs were distributed evenly throughout the physiological range without any contralateral bias. This difference in the distribution of preferred ITDs in IC and A1 had a major impact on the coding of ITDs at the population level: while a labeled-line decoder that considered the tuning of individual cells performed well on both IC and A1 responses, a two-channel decoder based on the overall activity in each hemisphere performed poorly on A1 responses relative to either labeled-line decoding of A1 responses or two-channel decoding of IC responses. These results suggest that the neural representation of ITDs in gerbils is transformed from IC to A1 and have important implications for how spatial location may be combined with other acoustic features for the analysis of complex auditory scenes.

Neurite outgrowth on electrospun PLLA fibers is enhanced by exogenous electrical stimulation

Objective. Both electrical stimuli (endogenous and exogenous) and topographical cues are instructive to axonal extension. This report, for the first time, investigated the relative dominance of directional topographical guidance cues and directional electrical cues to enhance and/or direct primary neurite extension. We hypothesized the combination of electrical stimulation with electrospun fiber topography would induce longer neurite extension from dorsal root ganglia neurons than the presence of electrical stimulation or aligned topography alone. Approach. To test the hypothesis, neurite outgrowth was examined on laminin-coated poly-L-lactide films or electrospun fibers (2 µm in diameter) in the presence or absence of electrical stimulation. Immunostained neurons were semi-automatically traced using Neurolucida software and morphology was evaluated. Main Results. Neurite extension increased 74% on the aligned fibers compared to film controls. Stimulation alone increased outgrowth by 32% on films or fibers relative to unstimulated film controls. The co-presentation of topographical (fibers) with biophysical (electrical stimulation) cues resulted in a synergistic 126% increase in outgrowth relative to unstimulated film controls. Field polarity had no influence on the directionality of neurites, indicating topographical cues are responsible for guiding neurite extension. Significance. Both cues (electrical stimulation and fiber geometry) are modular in nature and can be synergistically applied in conjunction with other common methods in regenerative medicine such as controlled release of growth factors to further influence axonal growth in vivo. The combined application of electrical and aligned fiber topographical guidance cues described herein, if translated in vivo, could provide a more supportive environment for directed and robust axonal regeneration following peripheral nerve injury.

Distance perception in the sound field reproduced by a linear loudspeaker array

When a sound field from a virtual sound source is reproduced by a linear loudspeaker array, a listener in the sound field can perceive the distance of the virtual source, as well as its direction. It has been known that the perception of distance is affected by many acoustic parameters, such as the loudness change, direct-to-early reflection energy ratio, and interaural level difference (ILD). Among them, ILD is the dominant cue to perceive distance when the source is located near the lateral side of the listener [Brungart and Rabinowitz, J. Acoust. Soc. Am. 106(3), Sept. 1999]. Nevertheless, ILD of the reproduced sound field are not identical to that of the target sound field, because the loudspeaker array reproducing the sound field has many practical limitations such as spatial aliasing and truncation of array aperture. To identify these artifacts, especially for the virtual source in a close proximity to the listener, a head-scattering model is constructed using a simple rigid sphere. The ILDs at various head locations are then calculated and compared to those of the target sound field. From the observations on ILD change, a driving function is modified to reconstruct ILDs of the target sound field.

Weighted cue integration in the rodent head direction system

How the brain combines information from different sensory modalities and of differing reliability is an important and still-unanswered question. Using the head direction (HD) system as a model, we explored the resolution of conflicts between landmarks and background cues. Sensory cue integration models predict averaging of the two cues, whereas attractor models predict capture of the signal by the dominant cue. We found that a visual landmark mostly captured the HD signal at low conflicts: however, there was an increasing propensity for the cells to integrate the cues thereafter. A large conflict presented to naive rats resulted in greater visual cue capture (less integration) than in experienced rats, revealing an effect of experience. We propose that weighted cue integration in HD cells arises from dynamic plasticity of the feed-forward inputs to the network, causing within-trial spatial redistribution of the visual inputs onto the ring. This suggests that an attractor network can implement decision processes about cue reliability using simple architecture and learning rules, thus providing a potential neural substrate for weighted cue integration.

Group tolerance, dispersal evolution, and the maintenance of polymorphism in recognition cues

In some systems, organisms form or join groups mediated by certain recognition cues. However, it is predicted that variability in such cues cannot be maintained as positive, frequency-dependent selection favors the dominant cue (Crozier’s paradox). We utilize a simple analytical model of 2 groups as well as computer simulations to find conditions where the coexistence (polymorphism) of 2 distinct recognition cues is maintained. We assume a species that forms reproductive groups and the adoption of a newborn individual into a group depends on that individual’s genotype (recognition cue) in relation to the group’s profile. We investigate the role of 2 factors affecting the level of isolation between groups, namely group tolerance toward deviant genotypes and dispersal between groups. Results from the analytical model show that high tolerance or high dispersal lead to the global fixation of a single genotype, whereas low group tolerance and low dispersal promote the globally stable coexistence of different genotypes. Interestingly, coexistence can only be global, with a different genotype dominating each group, or local, with 2 genotypes coexisting in one group, depending on the degree of tolerance and dispersal. Local coexistence, however, does not persist, when dispersal is allowed to evolve. In this case, low dispersal evolves, which stabilizes global coexistence but reduces local coexistence. If we expand the number of groups and assume spatially limited dispersal, global coexistence becomes a more likely outcome even under conditions where it was impossible in the 2-group system.

Directed cell migration in multi-cue environments

Cell migration plays a critical role in development, angiogenesis, immune response, wound healing and cancer metastasis. During these processes, cells are often directed to migrate towards targets by sensing aligned fibers or gradients in concentration, mechanical properties or electric field. Often times, cells must integrate migrational information from several of these different cues. While the cell migration behavior, signal transduction and cytoskeleton dynamics elicited by individual directional cues has been largely determined, responses to multiple directional cues are much less understood. However, initial work has pointed to several interesting behaviors in multi-cue environments, including competition and cooperation between cues to determine the migrational responses of cells. Much of the work on multi-cue sensing has been driven by the recent development of approaches to systematically and simultaneously control directional cues in vitro coupled with analysis and modeling that quantitatively describe those responses. In this review we present an overview of multi-cue directed migration with an emphasis on how cues compete or cooperate. We outline how multi-cue responses such as cue dominance might change depending on other environmental inputs. Finally, the challenges associated with the design of the environments to control multiple cues and the analysis and modeling of cell migration in multi-cue environments as well as some interesting biological questions associated with migration in complex environments are discussed. Understanding multi-cue migrational responses is critical to the mechanistic description of physiology and pathology, but also to the design of engineered tissues, where cell migration must be orchestrated to form specific tissue structures.

A Cholinergic Mechanism for Reward Timing within Primary Visual Cortex

Neurons in rodent primary visual cortex (V1) relate operantly conditioned stimulus-reward intervals with modulated patterns of spiking output, but little is known about the locus or mechanism of this plasticity. Here we show that cholinergic basal forebrain projections to V1 are necessary for the neural acquisition, but not the expression, of reward timing in the visual cortex of awake, behaving animals. We then mimic reward timing invitro by pairing white matter stimulation with muscarinic receptor activation at a fixed interval and show that this protocol results in the prolongation of electrically evoked spike train durations out to the conditioned interval. Together, these data suggest that V1 possesses the circuitry and plasticity to support reward time prediction learning and the cholinergic system serves as an important reinforcement signal which, invivo, conveys to the cortex the outcome of behavior.

Timbre and Speech Perception in Bimodal and Bilateral Cochlear-Implant Listeners

This study was designed to evaluate the contribution of temporal and spectral cues for timbre perception in listeners with a cochlear implant (CI) in one ear and low-frequency residual hearing in the contralateral ear (bimodal hearing), and listeners with two CIs. Specifically, it examined the relationship between timbre and speech perception in these two groups of listeners. It was hypothesized that, similar to speech recognition, temporal-envelope cues are dominant cues for timbre perception, and the reliance of spectral cues was reduced in both bimodal and bilateral CI users compared with that in normal-hearing listeners. It was further hypothesized that the patterns of results with regard to combined benefit would be similar between timbre and speech perception. Seven bimodal and five bilateral CI users participated. Sixteen stimuli that synthesized western musical instruments were used for the timbre-perception task. Sixteen consonants in the /aCa/ context and nine monophthongs in the /hVd/ context were used for the phoneme-recognition task. Each subject was tested on three listening conditions-individual device alone (single CI, or hearing aid [HA] alone) and combined use of devices (CI + HA, or 2CIs). For the timbre-perception task, each listener made judgments of dissimilarity between stimulus pairs. Multidimensional scaling analysis was performed to derive the coordinates of the dimensions that best fit the data. Correlational analyses were performed to relate the coordinates of each dimension and the temporal-envelope (impulsiveness) and spectral-envelope (spectral-centroid) features of the stimuli. For phoneme-recognition task, each listener identified the phoneme he or she heard by choosing an answer displayed on the computer screen. Overall percent correct phoneme-identification scores and percent information transmission for consonant and vowel features were calculated. There were strong correlations between impulsiveness and the first dimension (Dim 1) of the timbre space, but correlations between spectral centroid and the second dimension (Dim 2) were weak for all listening conditions for both groups of listeners. As a group, the combined use of devices did not significantly improve listeners' ability to perceive differences in musical timbre compared with the better single-device condition. Some of the bimodal and bilateral CI users showed a considerably strengthened correlation between spectral centroid and Dim 2 in the combined condition compared with a single CI or an HA. There was a lack of relationship between percent correct phoneme recognition and timbre perception for all listening conditions. However, there was a consistent pattern regarding the combined benefit between timbre perception and vowel recognition. In general, listeners who demonstrated combined benefit for vowel recognition also showed a considerable increase in correlation between spectral centroid and Dim 2 with the combined use of devices compared with the single-device conditions. Improved correlation was not evident for those who did not demonstrate combined benefit for vowel recognition. Similar to speech recognition, temporal envelope was a dominant cue for timbre perception in bimodal and bilateral CI users. In addition, there was a close relationship between timbre perception and vowel recognition with regard to combined benefit. The present findings suggest that speech recognition and timbre perception could be enhanced when listeners received different spectral cues from individual devices.

Acoustic cue integration in speech intonation recognition with cochlear implants.

The present article reports on the perceptual weighting of prosodic cues in question-statement identification by adult cochlear implant (CI) listeners. Acoustic analyses of normal-hearing (NH) listeners' production of sentences spoken as questions or statements confirmed that in English the last bisyllabic word in a sentence carries the dominant cues (F0, duration, and intensity patterns) for the contrast. Furthermore, these analyses showed that the F0 contour is the primary cue for the question-statement contrast, with intensity and duration changes conveying important but less reliable information. On the basis of these acoustic findings, the authors examined adult CI listeners' performance in two question-statement identification tasks. In Task 1, 13 CI listeners' question-statement identification accuracy was measured using naturally uttered sentences matched for their syntactic structures. In Task 2, the same listeners' perceptual cue weighting in question-statement identification was assessed using resynthesized single-word stimuli, within which fundamental frequency (F0), intensity, and duration properties were systematically manipulated. Both tasks were also conducted with four NH listeners with full-spectrum and noise-band-vocoded stimuli. Perceptual cue weighting was assessed by comparing the estimated coefficients in logistic models fitted to the data. Of the 13 CI listeners, 7 achieved high performance levels in Task 1. The results of Task 2 indicated that multiple sources of acoustic cues for question-statement identification were utilized to different extents depending on the listening conditions (e.g., full spectrum vs. spectrally degraded) or the listeners' hearing and amplification status (e.g., CI vs. NH).

Cues for Interpreting Distortion in Map Projections

The ability to recognize distortions of, for example, areas, angles, and landmass shapes in global-scale map projections, is an important part of critical map reading and use. This study investigates the cues used by individuals when they assess distortion on global-scale map projections. It was hypothesized that landmass shape would be a dominant cue used by individuals with no formal map projection training and that as projection knowledge increased the cues would become more systematic (e.g., use the graticule). Results indicate a tendency for novices to rely on landmass shape as a cue. Some evidence of a systematic evaluation of projections was also found.

Does listener weighting of binaural cues take advantage of the binaural statistics of reverberant environments?

A series of experiments quantified listeners' weighting of auditory spatial information conveyed by interaural differences of time (ITD) and level (ILD) across cue type (ITD-ILD “trading”) and over the durations of brief sounds (“temporal weighting”). Results demonstrated the dominance of cues, especially ITD, carried by the onsets of rapidly modulated or continuous tones. Whereas post-onset ITD information received little weight for such sounds, post-onset ILD was more influential, especially near sound offset [Stecker and Brown, JASA 127:3092-103. 2010]. As a consequence, the relative weighting of ITD and ILD changes systematically with modulation rate, with greater weighting of ILD in cases where post-onset ITD is unavailable [Stecker, Hear. Res. 268:202-12. 2010]. Greater weighting of post-onset ILD than ITD is consistent with observations of dramatic ITD distortion by echoes [Rakerd and Hartmann, JASA 78:524-33. 1985] and of a greater role for ILD in dynamic aspects of the precedence effect [Krumbholz and Nobbe, JASA 112:654-63. 2002] resulting from changes in the acoustic environment. Evidence regarding temporal weighting of ITD and ILD will be reviewed and compared to the statistics of binaural cue values across a variety of reverberant recordings. [Supported by NIH R03-DC009482, R01-DC011548, F31-DC010543, T32-DC000033]

The relative weight of shape and non-rigid motion cues in object perception: A model of the parameters underlying dynamic object discrimination

Shape and motion are two dominant cues for object recognition, but it can be difficult to investigate their relative quantitative contribution to the recognition process. In the present study, we combined shape and non-rigid motion morphing to investigate the relative contributions of both types of cues to the discrimination of dynamic objects. In Experiment 1, we validated a novel parameter-based motion morphing technique using a single-part three-dimensional object. We then combined shape morphing with the novel motion morphing technique to pairs of multipart objects to create a joint shape and motion similarity space. In Experiment 2, participants were shown pairs of morphed objects from this space and responded "same" on the basis of motion-only, shape-only, or both cues. Both cue types influenced judgments: When responding to only one cue, the other cue could be ignored, although shape cues were more difficult to ignore. When responding on the basis of both cues, there was an overall bias to weight shape cues more than motion cues. Overall, our results suggest that shape influences discrimination more than motion even when both cue types have been made quantitatively equivalent in terms of their individual discriminability.

Theoretic foundations of situating cognitive vision in robots and cognitive systems

Cognitive robots are supposed to execute different tasks, adapt to changes in the environment and cope with new situations. They shall operate in real-world settings. Hence, visual perception of the objects in the environment is an essential function. However, on the one hand there are robots using colour as dominant cue to cope with simple objects and on the other hand there are advanced computer vision methods that search through large data bases of images. What is usually missing to a robot are the higher level semantics of its world. To overcome this gap we analyse the specific requirement to the vision system given the context of cognitive robotics. We then propose a new approach to robot vision, which we termed situated vision in order to emphasise the situated and embodied aspects inherent in this domain. We are discussing requirements for such a situated vision system and provide a theory of cognitive functions that seem important to overcome limitations that appear when fixating only on the information that can be found in the visual input. Finally, we are explaining our understanding for the need of a common ontology on which these functions operate.

What causes the confusion patterns in speech perception?

It is widely believed that speech contains redundant cues which make it robust in noise. We have discovered that natural speech often contains conflicting cues that cause significant confusion patterns in speech perception. To demonstrate the impact of conflicting cues on the identification of consonant sounds, we selected four plosives /ta, ka, da, ga/ and four fricatives /si, Si, zi, Zi/ that show significant confusion with other sounds from a female high-performance talker in the LDC database and derived a set of test stimuli by removing the dominant cue and manipulating the conflicting cue. It was found that the consonants always morph to their competing sounds, once the dominant cue is unavailable. The confusion can be strengthened by enhancing the conflicting cue. These results demonstrate that the identification of consonant is dependent on a careful balancing between the dominant cue and the conflicting cues. Such prior knowledge about perceptual cues can be used to manipulate the perception of consonants, as demonstrated by the selected examples of nonsense syllables, meaningful words, and sentence.

Failure of the precedence effect with a noise-band vocoder

The precedence effect (PE) describes the ability to localize a direct, leading sound correctly when its delayed copy (lag) is present, though not separately audible. The relative contribution of binaural cues in the temporal fine structure (TFS) of lead-lag signals was compared to that of interaural level differences (ILDs) and interaural time differences (ITDs) carried in the envelope. In a localization dominance paradigm participants indicated the spatial location of lead-lag stimuli processed with a binaural noise-band vocoder whose noise carriers introduced random TFS. The PE appeared for noise bursts of 10 ms duration, indicating dominance of envelope information. However, for three test words the PE often failed even at short lead-lag delays, producing two images, one toward the lead and one toward the lag. When interaural correlation in the carrier was increased, the images appeared more centered, but often remained split. Although previous studies suggest dominance of TFS cues, no image is lateralized in accord with the ITD in the TFS. An interpretation in the context of auditory scene analysis is proposed: By replacing the TFS with that of noise the auditory system loses the ability to fuse lead and lag into one object, and thus to show the PE.

Reference Frame Preferences in Haptics Differ for the Blind and Sighted in the Horizontal but Not in the Vertical Plane

We investigated which reference frames are preferred when matching spatial language to the haptic domain. Sighted, low-vision, and blind participants were tested on a haptic-sentence-verification task where participants had to haptically explore different configurations of a ball and a shoe and judge the relation between them. Results from the spatial relation "above", in the vertical plane, showed that various reference frames are available after haptic inspection of a configuration. Moreover, the pattern of results was similar for all three groups and resembled patterns found for the sighted on visual sentence-verification tasks. In contrast, when judging the spatial relation "in front", in the horizontal plane, the blind showed a markedly different response pattern. The sighted and low-vision participants did not show a clear preference for either the absolute/relative or the intrinsic reference frame when these frames were dissociated. The blind, on the other hand, showed a clear preference for the intrinsic reference frame. In the absence of a dominant cue, such as gravity in the vertical plane, the blind might emphasise the functional relationship between the objects owing to enhanced experience with haptic exploration of objects.

Temporal and Spectral Cues for Musical Timbre Perception in Electric Hearing

The purpose of this study was to investigate musical timbre perception in cochlear-implant (CI) listeners using a multidimensional scaling technique to derive a timbre space. Methods Sixteen stimuli that synthesized western musical instruments were used (McAdams, Winsberg, Donnadieu, De Soete, & Krimphoff, 1995). Eight CI listeners and 15 normal-hearing (NH) listeners participated. Each listener made judgments of dissimilarity between stimulus pairs. Acoustical analyses that characterized the temporal and spectral characteristics of each stimulus were performed to examine the psychophysical nature of each perceptual dimension. For NH listeners, the timbre space was best represented in three dimensions, one correlated with the temporal envelope (log-attack time) of the stimuli, one correlated with the spectral envelope (spectral centroid), and one correlated with the spectral fine structure (spectral irregularity) of the stimuli. The timbre space from CI listeners, however, was best represented by two dimensions, one correlated with temporal envelope features and the other weakly correlated with spectral envelope features of the stimuli. Temporal envelope was a dominant cue for timbre perception in CI listeners. Compared to NH listeners, CI listeners showed reduced reliance on both spectral envelope and spectral fine structure cues for timbre perception.

On the relative dominance of global and local shape features in generalization: Moderating variables and general principles

There is a long-standing debate concerning the holistic or analytic nature of perceptual processing and whether the representation builds up from global to local or from local to global. Despite many fruitful contributions demonstrating the global and local levels in object recognition, little systematic attention has been directed at the local-global dominance in generalization and categorization. We investigated the global and local dominance of visual cues in a name generalization task. Two obvious features, one on a global scale and one on a more local scale, were implemented in the stimulus set. Stimuli were always 2-D shapes, generated by Boundary Descriptors. Participants were asked to infer new members of a category and could freely choose new instances in the stimulus set. By evaluating the inferred exemplars, the global-local dominance in generalization was studied. The results demonstrate that general conclusions are hard to draw based on the theoretically presumed allocation of the visual cues to the local or the global level of processing. However, by a thorough evaluation of the visual cues in terms of their regularities in the stimulus set, we were able to draw a general conclusion: Participants derive category membership by relying on regularities on the most global scale. Regularities on a more global scale are conceived as less coincidental features in the stimulus set, and therefore, they are preferred as a basis to infer new instances. Additionally, we tested the moderating influence of particular context variables like superordinate category ownership, planar rotations, and complexity on participants' reliance on global or local scale shape properties in generalization. Superordinate category ownership had no influence but more complex shapes and arbitrary planar rotations of the stimuli led to huge differences in participants' reliance on visual cues. We will discuss the results in light of some contemporary models of object recognition.

Computational Modeling of Statistical Learning: Effects of Transitional Probability Versus Frequency and Links to Word Learning.

Statistical learning mechanisms play an important role in theories of language acquisition and processing. Recurrent neural network models have provided important insights into how these mechanisms might operate. We examined whether such networks capture two key findings in human statistical learning. In Simulation 1, a simple recurrent network (SRN) performed much like human learners: it was sensitive to both transitional probability and frequency, with frequency dominating early in learning and probability emerging as the dominant cue later in learning. In Simulation 2, an SRN captured links between statistical segmentation and word learning in infants and adults, and suggested that these links arise because phonological representations are more distinctive for syllables with higher transitional probability. Beyond simply simulating general phenomena, these models provide new insights into underlying mechanisms and generate novel behavioral predictions.

Depth cue combination in spontaneous eye movements

Where we look when we scan visual scenes to obtain an understanding of the 3D world around us is a question of interest for both fundamental and applied research. Recently, it has been shown that depth is an important variable in driving eye movements: the directions of saccades tend to follow depth gradients (Wexler (2008), Janssen (2009)). Whether saccades are aligned with a single depth cue or a combination of depth cues is still unknown. And, in the latter case, it is interesting to ask whether saccades are based on similar combination rules as those that apply to depth perception. Moreover, these scanning eye movements across different depth planes are composed of two distinct components: conjugate shifts of gaze (saccades) and disjunctive movements changing the depth of fixation (vergence). And the same questions about the effect of depth cues still apply to vergence: various studies have reported that vergence is guided by the consciously perceived depth percept, whereas others report that vergence is based on depth cue(s). Here we studied what depth information is used to plan both saccades and vergence. We showed observers surfaces inclined in depth, in which perspective and disparity defined different plane orientations (both small (0°-45°) and large (90°,180°) conflicts). Observers' eye movements were recorded binocularly, while they scanned the surface. After the stimulus presentation, observers reported the perceived surface orientation using a joystick. We found saccade directions and perceived surface orientation use the same pattern of depth cue combination: a weighted linear cue combination for small conflicts and cue dominance for large cue conflicts. The weights assigned to each cue varied across subjects, but were strongly correlated for perception and saccades, within subjects. This correlation was maintained while manipulating cue reliability. Vergence on the other hand was dominated by the disparity cue.