Showing papers on "Salience (neuroscience) published in 2001"
TL;DR: This work shows a new type of perceptual learning, which occurs without attention, without awareness and without any task relevance, and suggests that a frequently presented feature sensitizes the visual system merely owing to its frequency, not its relevance or salience.
Abstract: The brain is able to adapt rapidly and continually to the surrounding environment, becoming increasingly sensitive to important and frequently encountered stimuli1,2,3,4. It is often claimed that this adaptive learning is highly task-specific, that is, we become more sensitive to the critical signals in the tasks we attend to5,6,7,8,9,10,11,12,13,14,15. Here, we show a new type of perceptual learning, which occurs without attention, without awareness and without any task relevance. Subjects were repeatedly presented with a background motion signal so weak that its direction was not visible; the invisible motion was an irrelevant background to the central task that engaged the subject's attention. Despite being below the threshold of visibility and being irrelevant to the central task, the repetitive exposure improved performance specifically for the direction of the exposed motion when tested in a subsequent suprathreshold test. These results suggest that a frequently presented feature sensitizes the visual system merely owing to its frequency, not its relevance or salience.
520 citations
TL;DR: It is proposed that the strategy of looking ahead to objects of future relevance supports the conscious percept of an environment seamless in time as well as in space.
330 citations
TL;DR: In this paper, a simple cognitive salience index, S=F/(N mP), that combines the two list task parameters (term frequency and its mean position in the lists) is presented together with the procedure for its calculation.
Abstract: The list task and its two parameters (term frequency and its mean position in the lists) are discussed here. A new simple cognitive salience index, S= F/(N mP), that combines the two list task parameters is presented together with the procedure for its calculation. The cognitive salience index is normed to vary between 1 and 0. The basic terms in every domain are the most salient. The salience index of the ideal most salient term has the figure 1 and that of the term not mentioned at all the value is 0. The cognitive salience index gives comparable results between different investigations, as it does not depend on the length of the individual lists. The cognitive salience index is compared with some earlier salience indices.
216 citations
TL;DR: It is concluded that feedback connections act in a non-linear fashion to boost the gain of the center mechanism and that they combine with horizontal connections to generate the center-surround interactions.
Abstract: The results of a previous study [Hupe et al. (1998) Nature, 394: 784–787] led us to conclude that feedback connections are important for differentiating a figure from the background, particularly in the case of low salience stimuli. This conclusion was principally based on the observation in area V3 neurons that inactivating MT by cooling led to a severe weakening of the center response and of the center-surround interactions, and that these effects were particularly strong for low salience stimuli. In the present paper, we first show that the results extend to areas V1 and V2. In particular, the inhibitory center-surround interactions in areas V1, V2 and V3 disappear almost completely in the absence of feedback input from MT for low salience stimuli, whereas the effects are much more limited for stimuli of middle and high salience. We then compare the results obtained in studies of feedback connections from MT to those obtained in a study of the feedback action of area V2 onto V1 neurons [Hupe et al. (2001) J. Neurophysiol., 85: 146–163], in which the same effects were observed on the center mechanism (decrease in response), but no effects were seen on the center-surround interactions. We conclude that feedback connections act in a non-linear fashion to boost the gain of the center mechanism and that they combine with horizontal connections to generate the center-surround interactions.
211 citations
TL;DR: In this article, a psychophysical model of how consumers make area comparison judgments is proposed, which involves consumers making effort-accuracy trade-offs that lead to heuristic processing of area judgments and systematic shape and size-related biases.
Abstract: Many product categories, from pizzas to real estate, present buyers with purchase decisions involving complex area judgments. Does a square look larger or smaller than a circle? How much smaller does a circle of 8-inch diameter look when compared to one with a 10-inch diameter? In this paper, we propose a psychophysical model of how consumers make area comparison judgments. The model involves consumers making effort-accuracy trade-offs that lead to heuristic processing of area judgments and systematic shape- and size-related biases.The model is based on four propositions: P1. Consumers make an initial comparison between two figures based on a single dimension; P2. The dimension of initial comparison--the primary dimension--is the one that is most salient to consumers, where salience is figure and context dependent; P3. Consumers insufficiently adjust an initial comparison using a secondary dimension, which we assume to be orthogonal to the primary dimension used for the initial comparison; and P4. The magnitude by which the initial comparison is adjusted is directly related to the relative salience of the secondary dimension versus the primary dimension.The model predicts that a single linear dimension inappropriately dominates the two-dimensional area comparison task and that contextual factors affect which linear dimension dominates the task. The relative use of the second dimension depends on its relative salience, which can be influenced in a variety of ways. The model extends the area estimation literature in cognitive psychology by exploring new biases in area estimation and is able to resolve controversial effects regarding which shape is perceived to be "bigger," the square or the circle, by incorporating contextual factors into model specifications.A set of six studies--five laboratory experiments and one field experiment--systematically test model predictions. Study 1 is a process study that shows that when two dimensions are available to make an area comparison judgment, people choose one of those to be the primary dimension, with the other being the secondary dimension. Furthermore, it shows that the choice of the primary dimension is dependent on its relative salience that can be contextually manipulated via manner of visual presentation.Studies 2 and 3 show how the use of a diagonal versus the side of a square (contextually determined) can affect whether a square is perceived to be smaller or larger than a circle of the same area. Study 3 extends the investigation to the domain of the price people are willing to pay for "pizzas" of different shapes, presented differently.Study 4, a field study, demonstrates external validity by showing that purchase quantities are greater when a circular package is expected to contain less than a rectangular package of the same volume in a domain where consumption goal is constant (cream cheese with a bagel).Studies 5 and 6 examine ways in which one can increase the salience of the secondary dimension, in a size estimation task, i.e., judging the rate of increase of area. While Study 5 does so via contextual visual cues (incorporating lines that draw one's attention to the underused dimension), Study 6 does the same using semantic cues that direct attention to a single dimension (e.g., diameter) or the total area and comparing these with a visual presentation of the figure.Overall, results suggest that the manner in which information is presented affects the relative salience of dimensions used to judge areas, and can influence the price consumers are willing to pay. Underlining the external validity of these findings, container shape can significantly affect quantity purchased and overall sales. The paper highlights biases in area comparison judgments as a function of area shape and size. The model is parsimonious, demonstrates good predictive ability, and explains seemingly contradictory results in the cognitive psychology literature. Implications for pricing, product design, packaging, and retailing are suggested.
167 citations
Book•
01 Jan 2001
TL;DR: This work presents evidence for attentional capture in the spatial and temporal domains and a multidisciplinary perspective on attentional control from the perspective of W.A. Reed.
Abstract: Neuroscience: Electrophysiological studies of reflexive attention, J.B. Hopfinger, G.R. Mangun Inhibition of return in monkey and man, R.M. Klein et al. Visual Cognition: Inattentional blindness and attentional capture - evidence for attention-based theories of visual salience, B.S. Gibson, M.A. Peterson Involuntary orienting to flashing distractors in delayed search?, H. Pashler Attentional capture in the spatial and temporal domains, H.E. Egeth et al Attentional and oculomotor capture, J. Theeuwes, R. Godijn Attention capture, orienting, and awareness, S.B. Most, D.J. Simons. Multiple Modalities: Using pre-pulse inhibition to study attentional capture - a warning about pre-pulse correlations, J.T. Mordkoff, H. Barth Temporal expectancies, capture, and timing in auditory sequences, M.R. Jones Crossmodal attentional capture - a controversy resolved?, C. Spence. Developmental: Testing models of attentional capture during early infancy, J.L. Dannemiller Attentional capture, attentional control, and aging, A.F. Kramer et al. Individual Differences: A multidisciplinary perspective on attentional control, D. Derryberry, M.A. Reed Capacity, control and conflict - an individual differences perspective on attentional capture, A.R.A. Conway, M.J. Kane. Dynamical Systems/Evolution: A dynamic, evolutionary perspective on attention capture, W.A. Johnson, D.L. Stayer.
164 citations
TL;DR: A strong negative relationship was obtained between attentional breadth and the latency with which perceptual changes were detected; observers with broader attentional windows detected changes faster.
Abstract: Previous research has shown that changes to scenes are often surprisingly hard to detect. The research reported here investigated the relationship between individual differences in attention and change detection. We did this by assessing participantś breadth of attention in a functional field of view task (FFOV) and relating this measure to the speed with which individuals detected changes in scenes. We also examined how the salience, meaningfulness, and eccentricity of the scene changes affected perceptual change performance. In order to broaden the range of individual differences in attentional breadth, both young and old adults participated in the study. A strong negative relationship was obtained between attentional breadth and the latency with which perceptual changes were detected; observers with broader attentional windows detected changes faster. Salience and eccentricity had large effects on change detection, but meaning aided the performance of young adults only and only when changes also had low salience.
114 citations
TL;DR: Part-based representations explain various aspects of human visual cognition, including figure-ground assignment, memory for shapes, visual search for shapes and the perception of transparency, and the allocation of visual attention to objects as discussed by the authors.
Abstract: Human vision organizes object shapes in terms of parts and their spatial relationships. Converging experimental evidence suggests that parts are computed rapidly and early in visual processing. We review theories of how human vision parses shapes. In particular, we discuss the minima rule for finding part boundaries on shapes, geometric factors for creating part cuts, and a theory of part salience. We review empirical evidence that human vision parses shapes into parts, and show that parts-based representations explain various aspects of our visual cognition, including figure-ground assignment, judgments of shape similarity, memory for shapes, visual search for shapes, the perception of transparency, and the allocation of visual attention to objects.
99 citations
TL;DR: This annotation supports the proposal that faces are special, but suggests that their identification makes use of general-purpose cortical systems that are implicated in high-level vision and also in memory and learning more generally.
Abstract: Face recognition is often considered to be a modular (encapsulated) function. This annotation supports the proposal that faces are special, but suggests that their identification makes use of general-purpose cortical systems that are implicated in high-level vision and also in memory and learning more generally. These systems can be considered to function within two distinct cortical streams: a medial stream (for learning and salience of faces encountered) and a lateral stream (for distributed representations of visual properties and identities of faces). Function in the lateral stream, especially, may be critically dependent on the normal development of magnocellular vision. The relevance of face recognition anomalies in three developmental syndromes (Autism, Williams syndrome, and Turner syndrome) and the two-route model sketched above is considered.
71 citations
01 Oct 2001
TL;DR: In this article, the authors defined cognitive tunneling as the effect where observers tend to focus attention on information from specific areas of a display to the exclusion of information presented outside of these highly attended areas.
Abstract: This proposal describes a two-part study which illustrates “cognitive tunneling” as it affects information gathering and change detection in computer-generated terrain displays. We define cognitive tunneling as the effect where observers tend to focus attention on information from specific areas of a display to the exclusion of information presented outside of these highly attended areas. Previous research suggests that cognitive tunneling is induced by more immersive or egocentric visual displays and results in poorer information extraction and situation awareness as compared to an exocentric display of the same information. The experiment discussed here determined that failure of the observers to integrate information across the two views of the immersed display was the primary cause of the cognitive tunneling effect. In addition, participants’ abilities to detect changes to objects in the environment were affected by the type of change as well as the salience of its presentation within the view.
69 citations
TL;DR: The results demonstrate that ideal-observer analysis can be extended to measure the visual information mediating saccadic target-selection decisions during visual search, which enables direct comparison of saccades and perceptual efficiencies.
Abstract: In previous studies of saccadic targeting, the issue how visually guided saccades to unambiguous targets are programmed and executed has been examined. These studies have found different degrees of guidance for saccades depending on the task and task difficulty. In this study, we use ideal-observer analysis to estimate the visual information used for the first saccade during a search for a target disk in noise. We quantitatively compare the performance of the first saccadic decision to that of the ideal observer (ie absolute efficiency of the first saccade) and to that of the associated final perceptual decision at the end of the search (ie relative efficiency of the first saccade). Our results show, first, that at all levels of salience tested, the first saccade is based on visual information from the stimulus display, and its highest absolute efficiency is approximately 20%. Second, the efficiency of the first saccade is lower than that of the final perceptual decision after active search (with eye movements) and has a minimum relative efficiency of 19% at the lowest level of saliency investigated. Third, we found that requiring observers to maintain central fixation (no saccades allowed) decreased the absolute efficiency of their perceptual decision by up to a factor of two, but that the magnitude of this effect depended on target salience. Our results demonstrate that ideal-observer analysis can be extended to measure the visual information mediating saccadic target-selection decisions during visual search, which enables direct comparison of saccadic and perceptual efficiencies.
TL;DR: It is argued that the neural processes associated with the particular brand-choice stimulus can be separated into identifiable stages through observation of MEG responses and knowledge of functional anatomy.
Abstract: We used magnetoencephalography (MEG) to study the dynamics of neural responses in eight subjects engaged in shopping for day-to-day items from supermarket shelves. This behavior not only has personal and economic importance but also provides an example of an experience that is both personal and shared between individuals. The shopping experience enables the exploration of neural mechanisms underlying choice based on complex memories. Choosing among different brands of closely related products activated a robust sequence of signals within the first second after the presentation of the choice images. This sequence engaged first the visual cortex (80-100 ms), then as the images were analyzed, predominantly the left temporal regions (310-340 ms). At longer latency, characteristic neural activetion was found in motor speech areas (500-520 ms) for images requiring low salience choices with respect to previous (brand) memory, and in right parietal cortex for high salience choices (850-920 ms). We argue that the neural processes associated with the particular brand-choice stimulus can be separated into identifiable stages through observation of MEG responses and knowledge of functional anatomy.
Book•
30 Apr 2001
TL;DR: A review of perception-based definitions of saliency can be found in this article, where a model of inconsistency-salience is presented. But this model is not applicable to print advertising.
Abstract: List of Figures. List of Tables. Preface. 1. Introduction to the Concept of Salience. 2. Review of Perception-Based Definitions of Salience. 3. A Model of Incongruity-Salience. 4. Consumer Awareness of Print Advertisements. Index.
TL;DR: Perceptual fading of texture targets on similarly textured backgrounds was studied in relation to stimulus salience using texture patterns defined by orientation contrast, shape contrast, and order contrast, which appeared to change gradually in orientation, shape, and spatial arrangement, thereby assuming the properties of the background.
TL;DR: The results showed that search was not affected by the presence of the preceding distractors when the target was relatively low in salience, which suggests that visual marking can increase the efficiency of visual search by decreasing the size of the search set.
Abstract: In the present study, the gap paradigm originally developed by Watson and Humphreys (1997) was used to investigate whether the process of visual marking can influence the perceptual salience of a target in visual search. Consistent with previous studies (Watson & Humphreys, 1997), the results showed that search was not affected by the presence of the preceding distractors when the target was relatively low in salience. This finding suggests that visual marking can increase the efficiency of visual search by decreasing the size of the search set. However, more important, the results also showed that search was affected by the presence of the preceding distractors when the target was relatively high in salience. This finding suggests that visual marking may be limited in its ability to increase the perceptual salience of the target. Together, the results of the present study suggest that the effectiveness of visual marking may vary as a function of search context.
TL;DR: The efficiency and the effectiveness with which high-salience subsets of features can be identified in the context of ill-understood and potentially noisy real-world data are examined.
Abstract: We assess the relative merits of a number of techniques designed to determine the relative salience of the elements of a feature set with respect to their ability to predict a category outcome—for example, which features of a character contribute most to accurate character recognition. A number of different neural-net-based techniques have been proposed (by us and others) in addition to a standard statistical technique, and we add a technique based on inductively generated decision trees. The salience of the features that compose a proposed set is an important problem to solve efficiently and effectively, not only for neural computing technology but also in order to provide a sound basis for any attempt to design an optimal computational system. The focus of this study is the efficiency and the effectiveness with which high-salience subsets of features can be identified in the context of ill-understood and potentially noisy real-world data. Our two simple approaches, weight clamping using a neural network and feature ranking using a decision tree, generally provide a good, consistent ordering of features. In addition, linear correlation often works well.
TL;DR: The results suggest that when an important signal appears during attentional focalization, the thalamus interrupts current focalization and permits the compilation of an attentional program in the midbrain aiming at generating an orienting response towards the source of this signal.
Abstract: When attention is involuntarily drawn in a direction different to that of the target, slower motor response times are observed (i.e. the meridian effect). Previous data suggested that the thalamus might participate in the generation of visual salience. What may be the role of the thalamus in the capture by luminance transients when attentional control is in action? A single experiment was administrated in a group of ten healthy volunteers as well as in a group of three patients with unilateral thalamic infarcts. Subjects participated in a task where attentional control was interrupted by a distractor. The meridian effect was present only in the performance of the healthy volunteers and when distractors occurred in the ipsilesional (intact) hemifield of the thalamic patients. These results suggest that when an important signal appears during attentional focalization, the thalamus interrupts current focalization and permits the compilation of an attentional program in the midbrain aiming at generating an orienting response towards the source of this signal.
TL;DR: It is suggested that selective attention facilitates synchronization of neural activity in the frequency range above 20 Hz, the gamma-band, and the notion of a link between induced gamma- band responses and attentive, sensory stimulus processing is supported.
Abstract: Synchronized neural activity in the frequency range above 20 Hz, the gamma-band, has been proposed as a signature of temporal feature binding. Here we suggest that selective attention facilitates synchronization of neural activity. Selective attention can be guided by bottom-up, stimulus driven, or top-down task-driven processes. Both processes will cause that stimuli are processed preferentially. While bottom-up processes might facilitate synchronization of neurons due to the salience of the stimulus, top-down processes may bias information selection by facilitating synchronization of neurons coding a certain location in space and/or of neurons related to the processing of certain features. Animal as well as human EEG studies support the notion of a link between induced gamma-band responses and attentive, sensory stimulus processing.
01 Jan 2001
TL;DR: This paper proposes a hierarchy of salience criteria linked to an algorithm that detects salient objects, as well as guidelines for grouping algorithms, and concludes on the usability of such heuristics in actual systems.
Abstract: This paper deals with the pragmatic interpretation of multimodal referring expressions in man-machine dialogue systems We show the importance of building up a structure of the visual context at a semantic level, in order to enrich the significant possibilities of interpretations and to make possible the fusion of this structure with the ones obtained from the linguistic and gesture semantic analyses Visual salience and perceptual grouping are two notions that guide such a structuring We thus propose a hierarchy of salience criteria linked to an algorithm that detects salient objects, as well as guidelines for grouping algorithms We show how the integration of the results of all these algorithms is a complex problem We propose simple heuristics to reduce this complexity and we conclude on the usability of such heuristics in actual systems
TL;DR: In this article, a topological approach has been proposed to describe precisely the nature and rules of perceptual organization, and evidence supporting topological perception will be illustrated in topics of visual sensitivity, apparent motion, illusory conjunctions, and the relative salience of d...
Abstract: In addressing the most fundamental question of “Where visual processing begins”, all theories of perception can be segregated into two contrasting lines of thinking: “early feature-analysis” (i.e., from local to global processing) and “early holistic registration” (i.e., from global to local processing). The problem of feature binding is then essentially a consequence of the particular local-to-global assumption. However, from the global-to-local perspective, the problem of feature binding may be a wrong question to ask to begin with, while the Gestalt concept of perceptual organization serves to reverse this inverted position. Inspired by the analysis of invariants over transformations, particularly shape-changing transformations, a topological approach has been proposed to describe precisely the nature and rules of perceptual organization. Evidence supporting topological perception will be illustrated in topics of visual sensitivity, apparent motion, illusory conjunctions, and the relative salience of d...
TL;DR: These studies provide converging evidence for a functional distinction between unimodal and multimodal stimulation during early development and suggest that ecological validity can be enhanced when research findings are generalized appropriately to the natural environment and are not overgeneralized across stimulus properties, tasks, or contexts.
Abstract: Studies of infant development concerned with the emergence of specific perceptual or cognitive abilities have typically focused on responsiveness in only one sensory modality. Research on infant perception, learning, and memory often attempts to reduce multimodal stimulation to "noise" and to control or omit stimulation from other sensory modalities in experimental designs. This type of unimodal research, although important, may not generalize well to the behavior of infants in the multimodal context of the everyday world. Research from animal and human development is reviewed that documents that significant differences in infants' perceptual skills and abilities can be observed under conditions of unimodal versus multimodal stimulation. These studies provide converging evidence for a functional distinction between unimodal and multimodal stimulation during early development and suggest that ecological validity can be enhanced when research findings are generalized appropriately to the natural environment...
01 Jan 2001
TL;DR: The algorithm is based on empirical studies of how humans refer to objects in a shared workspace and is capable of generating a variety of referring expressions, where the kind of NP is co-determined by the accessibility of the target object, the presence or absence of a relatum as well as the possible inclusion of a pointing gesture.
Abstract: In this paper an algorithm for the generation of referring expressions in a multimodal setting is presented. The algorithm is based on empirical studies of how humans refer to objects in a shared workspace. The main ingredients of the algorithm are the following. First, the addition of deictic pointing gestures, where the decision to point is determined by two factors: the effort of pointing (measured in terms of the distance to and size of the target object) as well as the effort required for a full linguistic description (measured in terms of number of required properties and relations). Second, the algorithm explicitly keeps track of the current focus of attention, in such a way that objects which are closely related to the object which was most recently referred to are more prominent than objects which are farther away. To decide which object are ‘closely related’ we make use of the concept of perceptual grouping. Finally, each object in the domain is assigned a three-dimensional salience weight indicating whether it is linguistically and/or inherently salient and whether it is part of the current focus of attention. The resulting algorithm is capable of generating a variety of referring expressions, where the kind of NP is co-determined by the accessibility of the target object (in terms of salience), the presence or absence of a relatum as well as the possible inclusion of a pointing gesture.
TL;DR: It is demonstrated that a Bayesian confidence propagation neural network with learning time constant modulated in this way exhibits enhanced recall of an item tagged as salient, and an inverted U-shape response to overall plasticity.
01 Jan 2001
01 Jan 2001
TL;DR: The algorithm is based on empirical studies of how humans refer to objects in a shared workspace and is capable of generating a variety of referring expressions, where the kind of NP is co-determined by the accessibility of the target object, the presence or absence of a relatum as well as the possible inclusion of a pointing gesture.
Abstract: In this paper an algorithm for the generation of referring expressions in a multimodal setting is presented. The algorithm is based on empirical studies of how humans refer to objects in a shared workspace. The main ingredients of the algorithm are the following. First, the addition of deictic pointing gestures, where the decision to point is determined by two factors: the effort of pointing (measured in terms of the distance to and size of the target object) as well as the effort required for a full linguistic description (measured in terms of number of required properties and relations). Second, the algorithm explicitly keeps track of the current focus of attention, in such a way that objects which are closely related to the object which was most recently referred to are more prominent than objects which are farther away. To decide which object are ‘closely related’ we make use of the concept of perceptual grouping. Finally, each object in the domain is assigned a three-dimensional salience weight indicating whether it is linguistically and/or inherently salient and whether it is part of the current focus of attention. The resulting algorithm is capable of generating a variety of referring expressions, where the kind of NP is co-determined by the accessibility of the target object (in terms of salience), the presence or absence of a relatum as well as the possible inclusion of a pointing gesture.
TL;DR: In this article, an extension to "detail fusion" through match and salience analysis is proposed, where four details or edge orientations commonly considered are extended to twenty-four textures.
Abstract: An extension to 'detail fusion' through match and salience analysis is proposed. The four details or edge orientations commonly considered are extended to twenty-four textures. A comparison of the results of both schemes is made.
TL;DR: This work proposes an auto-scaled, extended neighborhood-based context model to obtain reliable measurements of relative saliency features and shows that the proposed model is capable of generating predicates more consistent with perceived saliency.
Proceedings Article•
01 Jan 2001
TL;DR: An algorithm for generating multimodal referring expressions, based on empirical data, and a threedimensional notion of salience incorporating linguistic, focus and inherent salience is described.
Abstract: We describe an algorithm for generating multimodal referring expressions, based on empirical data. The main novelties are (1) a decision to point based on both the efficiency of pointing (Fitt’s law) and the inefficiency of a full linguistic description, (2) the explicit tracking of the ’focus of attention’, and (3) a threedimensional notion of salience incorporating linguistic, focus and inherent salience.
25 Oct 2001
TL;DR: The results of a series of recent experiments in monkeys performing pop-out visual search tasks suggest that the frontal eye field functions as a map of visual salience.
Abstract: Models of attention and saccade target selection propose that within the brain there is a topographic map of visual salience that selects, through a winner-take-all mechanism, locations for further processing. The results of a series of recent experiments in monkeys performing pop-out visual search tasks suggest that the frontal eye field (FEF) functions as a map of visual salience. FEF is located at the interface of sensory and motor processing and participates in the transformation of visual information into a command to move the eyes. Visually responsive neurons in FEF identify conspicuous objects in a search array regardless of the feature that renders conspicuousness. Furthermore, selection occurs at a constant interval following search array presentation and is dissociated from saccade production. The finding of a visual salience map in FEF validates models of visual selection and can serve to guide future empirical and theoretical investigations.