Representing the egocentric auditory space: Relationships of surrounding region concepts

We investigated the representation of azimuthal directions of sound sources under two different conditions. In the first experiment, we examined the participants' mental representation of sound source directions via similarity judgments. Auditory stimuli originating from sixteen loudspeakers positioned equidistantly around the participant were presented in pairs, with the first stimulus serving as the anchor, and thereby providing the context for the second stimulus. For each pair of stimuli, participants had to rate the sound source directions as either similar or dissimilar. In the second experiment, the same participants categorized single sound source directions using verbal direction labels (front, back, left, right, and combinations of any two of these). In both experiments, the directions within the front and back regions were more distinctively categorized than those on the sides, and the sides' categories included more directions than those of the front or back. Furthermore, we found evidence that the left-right decision comprises the basic differentiation of the surrounding regions. These findings illustrate what seem to be central features of the representation of directions in auditory space.     

Misperception of exocentric directions in auditory space

Previous studies have demonstrated large errors (over 30 degrees ) in visually perceived exocentric directions (the direction between two objects that are both displaced from the observer's location; e.g., Philbeck et al. [Philbeck, J. W., Sargent, J., Arthur, J. C., & Dopkins, S. (2008). Large manual pointing errors, but accurate verbal reports, for indications of target azimuth. Perception, 37, 511-534]). Here, we investigated whether a similar pattern occurs in auditory space. Blindfolded participants either attempted to aim a pointer at auditory targets (an exocentric task) or gave a verbal estimate of the egocentric target azimuth. Targets were located at 20-160 degrees azimuth in the right hemispace. For comparison, we also collected pointing and verbal judgments for visual targets. We found that exocentric pointing responses exhibited sizeable undershooting errors, for both auditory and visual targets, that tended to become more strongly negative as azimuth increased (up to -19 degrees for visual targets at 160 degrees ). Verbal estimates of the auditory and visual target azimuths, however, showed a dramatically different pattern, with relatively small overestimations of azimuths in the rear hemispace. At least some of the differences between verbal and pointing responses appear to be due to the frames of reference underlying the responses; when participants used the pointer to reproduce the egocentric target azimuth rather than the exocentric target direction relative to the pointer, the pattern of pointing errors more closely resembled that seen in verbal reports. These results show that there are similar distortions in perceiving exocentric directions in visual and auditory space.     

Temporal constraints on apparent motion in auditory space

The hypothesis that the extent of spatial separation between successive sound events directly affects the perception of time intervals between these events was tested using an apparent motion paradigm. Subjects listened to four-tone pitch patterns whose individual tones were sounded alternately at one of two loudspeaker positions, and they adjusted the alternation rate until they could no longer distinguish the four-tone ordering of the pattern. Four horizontal and two vertical loudspeaker separations were tested. Results indicate a direct relation between horizontal separation and the critical stimulus onset asynchrony (SOA) between successive tones within a pattern. At the critical SOA, subjects reported hearing not a four-tone pattern, but two pairs of two-note groups overlapping in time. The findings are discussed in the context .of auditory spatial processing mechanisms and possible sensory-specific representational constraints.     

Cognitive representation of auditory space in blind football experts

ObjectivesWe compared the mental representation of sound directions in blind football players, blind non-athletes and sighted individuals.DesignStanding blindfolded in the middle of a circle with 16 loudspeakers, participants judged whether the directions of two subsequently presented sounds were similar or not.MethodStructure dimensional analysis (SDA) was applied to reveal mean cluster solutions for the groups.ResultsHierarchical cluster analysis via SDA resulted in distinct representation structures of sound directions. The blind football players' mean cluster solution consisted of pairs of neighboring directions. The blind non-athletes also clustered the directions in pairs, but included non-adjacent directions. In the sighted participants' structure, frontal directions were clustered pairwise, the absolute back was singled out, and the side regions accounted for more directions.ConclusionsOur results suggest that the mental representation of egocentric auditory space is influenced by sight and by the level of expertise in auditory-based orientation and navigation.     

On the role of space and time in auditory processing

Unlike visual and tactile stimuli, auditory signals that allow perception of timbre, pitch and localization are temporal. To process these, the auditory nervous system must either possess specialized neural machinery for analyzing temporal input, or transform the initial responses into patterns that are spatially distributed across its sensory epithelium. The former hypothesis, which postulates the existence of structures that facilitate temporal processing, is most popular. However, I argue that the cochlea transforms sound into spatiotemporal response patterns on the auditory nerve and central auditory stages; and that a unified computational framework exists for central auditory, visual and other sensory processing. Specifically, I explain how four fundamental concepts in visual processing play analogous roles in auditory processing.     

Perceptual load influences auditory space perception in the ventriloquist aftereffect

A period of exposure to trains of simultaneous but spatially offset auditory and visual stimuli can induce a temporary shift in the perception of sound location. This phenomenon, known as the ‘ventriloquist aftereffect’, reflects a realignment of auditory and visual spatial representations such that they approach perceptual alignment despite their physical spatial discordance. Such dynamic changes to sensory representations are likely to underlie the brain’s ability to accommodate inter-sensory discordance produced by sensory errors (particularly in sound localization) and variability in sensory transduction. It is currently unknown, however, whether these plastic changes induced by adaptation to spatially disparate inputs occurs automatically or whether they are dependent on selectively attending to the visual or auditory stimuli. Here, we demonstrate that robust auditory spatial aftereffects can be induced even in the presence of a competing visual stimulus. Importantly, we found that when attention is directed to the competing stimuli, the pattern of aftereffects is altered. These results indicate that attention can modulate the ventriloquist aftereffect.     

Representing AIDS

AIDS has contributed to changes in how our society constructs its image of death. In the early 1980s Philippe Ariès argued that death and the symbols surrounding it had been “relegated to the secret, private space of the home or the hospital.” With the coming of AIDS, death demands its place in the public mind - and eye. Many artists have devoted their talents to making AIDS visible. In doing so, they have resurrected many questions about sexuality and mortality. This paper discusses several examples of current AIDS art and places them in a wider cultural and historical context.     

Representing causation

The dynamics model, which is based on L. Talmy's (1988) theory of force dynamics, characterizes causation as a pattern of forces and a position vector. In contrast to counterfactual and probabilistic models, the dynamics model naturally distinguishes between different cause-related concepts and explains the induction of causal relationships from single observations. Support for the model is provided in experiments in which participants categorized 3-D animations of realistically rendered objects with trajectories that were wholly determined by the force vectors entered into a physics simulator. Experiments 1-3 showed that causal judgments are based on several forces, not just one. Experiment 4 demonstrated that people compute the resultant of forces using a qualitative decision rule. Experiments 5 and 6 showed that a dynamics approach extends to the representation of social causation. Implications for the relationship between causation and time are discussed.     

Representing Bodies

According to the bodily awareness thesis (BAT), awareness of one's own body is a necessary condition for the acquisition and possession of concepts of primary qualities such as force and shape. I discuss two arguments for this thesis. The acquisition argument for BAT focuses on the role of bodily sensation and action in the acquisition of the concept of force. I suggest that this argument requires us to conceive of the content of sensation as both representational and non–conceptual. The objective reality argument for BAT claims that awareness of one's own body is an essential component of those experiences which are required for a proper grasp of concepts of primary qualities. I conclude by arguing, in opposition to Sartre and Merleau–Ponty, that there is no incoherence in the idea that one's body is a thing among other things.     

Representing the meanings of object and action words: the featural and unitary semantic space hypothesis

This paper presents the Featural and Unitary Semantic Space (FUSS) hypothesis of the meanings of object and action words. The hypothesis, implemented in a statistical model, is based on the following assumptions: First, it is assumed that the meanings of words are grounded in conceptual featural representations, some of which are organized according to modality. Second, it is assumed that conceptual featural representations are bound into lexico-semantic representations that provide an interface between conceptual knowledge and other linguistic information (syntax and phonology). Finally, the FUSS model employs the same principles and tools for objects and actions, modeling both domains in a single semantic space. We assess the plausibility of the model by showing that it can capture generalizations presented in the literature, in particular those related to category-related deficits, and show that it can predict semantic effects in behavioral experiments for object and action words better than other models such as Latent Semantic Analysis (Landauer & Dumais, 1997) and similarity metrics derived from Wordnet (Miller & Fellbaum, 1991).     

Reasoning and Representing

I argue that logical understanding is not propositional knowledgebut is rather a species of practical knowledge. I further arguethat given the best explanation of logical understanding someversion or another of inferential role semantics must be the correct account of the determinants of logical content.     

Representing God's Presence

The article tackles two myths: the modern myth that God has vanished from human life, and the religious myth that the apostles, patriarchs, mystics and martyrs were in a more privileged position vis-´-vis God than we are. Dalferth argues that God has never been more present than today, has never been less hidden than today, and develops the thessis that the importance of God being present is central to the Christian understanding of God. Christian faith is faith in a present reality, not a set of beliefs about past events. The implications of this for the task of Christian communication are clear: the prime interest of Christian communication is to help those to whom it is addressed to develop a sense of the presence of God.     

Representing properties locally

Theories of knowledge such as feature lists, semantic networks, and localist neural nets typically use a single global symbol to represent a property that occurs in multiple concepts. Thus, a global symbol represents mane across HORSE, PONY, and LION. Alternatively, perceptual theories of knowledge, as well as distributed representational systems, assume that properties take different local forms in different concepts. Thus, different local forms of mane exist for HORSE, PONY, and LION, each capturing the specific form that mane takes in its respective concept. Three experiments used the property verification task to assess whether properties are represented globally or locally (e.g., Does a PONY have mane?). If a single global form represents a property, then verifying it in any concept should increase its accessibility and speed its verification later in any other concept. Verifying mane for PONY should benefit as much from having verified mane for LION earlier as from verifying mane for HORSE. If properties are represented locally, however, verifying a property should only benefit from verifying a similar form earlier. Verifying mane for PONY should only benefit from verifying mane for HORSE, not from verifying mane for LION. Findings from three experiments strongly supported local property representation and ruled out the interpretation that object similarity was responsible (e.g., the greater overall similarity between HORSE and PONY than between LION and PONY). The findings further suggest that property representation and verification are complicated phenomena, grounded in sensory-motor simulations.     

Meditation alters representations of peripersonal space: Evidence from auditory evoked potentials

Meditation commonly gives rise to the feeling that the self and the surrounding world are no longer separate, as if the boundary between them has dissolved. We propose this may occur due to alterations in representations of peripersonal space (PPS), the reachable space surrounding the body which is integral to a sense of where one’s bodily “self” is located in space. Thirty-one participants completed an auditory oddball paradigm before and after a guided meditation, during which we measured their P3 evoked potential, a marker of attentional salience. Pre-meditation, participants exhibited an enhanced attentional response to stimuli presented within PPS, relative to beyond PPS. Post-meditation, this PPS attentional enhancement was negated, with no distinction between responses to stimuli within versus beyond PPS. The results suggest that meditation leads to a constriction of PPS boundaries, even in novice meditators, elucidating one potential cause of the perceptual changes associated with meditation.     

The shape of ears to come: dynamic coding of auditory space

In order to pinpoint the location of a sound source, we make use of a variety of spatial cues that arise from the direction-dependent manner in which sounds interact with the head, torso and external ears. Accurate sound localization relies on the neural discrimination of tiny differences in the values of these cues and requires that the brain circuits involved be calibrated to the cues experienced by each individual. There is growing evidence that the capacity for recalibrating auditory localization continues well into adult life. Many details of how the brain represents auditory space and of how those representations are shaped by learning and experience remain elusive. However, it is becoming increasingly clear that the task of processing auditory spatial information is distributed over different regions of the brain, some working hierarchically, others independently and in parallel, and each apparently using different strategies for encoding sound source location.