Levels of processing during non-conscious perception: a critical review of visual masking

Understanding the extent and limits of non-conscious processing is an important step on the road to a thorough understanding of the cognitive and cerebral correlates of conscious perception. In this article, we present a critical review of research on subliminal perception during masking and other related experimental conditions. Although initially controversial, the possibility that a broad variety of processes can be activated by a non-reportable stimulus is now well established. Behavioural findings of subliminal priming indicate that a masked word or digit can have an influence on perceptual, lexical and semantic levels, while neuroimaging directly visualizes the brain activation that it evokes in several cortical areas. This activation is often attenuated under subliminal presentation conditions compared to consciously reportable conditions, but there are sufficiently many exceptions, in paradigms such as the attentional blink, to indicate that high activation, per se, is not a sufficient condition for conscious access to occur. We conclude by arguing that for a stimulus to reach consciousness, two factors are jointly needed: (i) the input stimulus must have enough strength (which can be prevented by masking) and (ii) it must receive top-down attention (which can be prevented by drawing attention to another stimulus or task). This view leads to a distinction between two types of non-conscious processes, which we call subliminal and preconscious. According to us, maintaining this distinction is essential in order to make sense of the growing neuroimaging data on the neural correlates of consciousness.     

Visual perception from the perspective of a representational,non-reductionistic,level-dependent account of perception and conscious awareness

This article proposes a new model to interpret seemingly conflicting evidence concerning the correlation of consciousness and neural processes. Based on an analysis of research of blindsight and subliminal perception, the reorganization of elementary functions and consciousness framework suggests that mental representations consist of functions at several different levels of analysis, including truly localized perceptual elementary functions and perceptual algorithmic modules, which are interconnections of the elementary functions. We suggest that conscious content relates to the ‘top level’ of analysis in a ‘situational algorithmic strategy’ that reflects the general state of an individual. We argue that conscious experience is intrinsically related to representations that are available to guide behaviour. From this perspective, we find that blindsight and subliminal perception can be explained partly by too coarse-grained methodology, and partly by top-down enhancing of representations that normally would not be relevant to action.     

Can the meaning of multiple words be integrated unconsciously?

What are the limits of unconscious language processing? Can language circuits process simple grammatical constructions unconsciously and integrate the meaning of several unseen words? Using behavioural priming and electroencephalography (EEG), we studied a specific rule-based linguistic operation traditionally thought to require conscious cognitive control: the negation of valence. In a masked priming paradigm, two masked words were successively (Experiment 1) or simultaneously presented (Experiment 2), a modifier (‘not’/‘very’) and an adjective (e.g. ‘good’/‘bad’), followed by a visible target noun (e.g. ‘peace’/‘murder’). Subjects indicated whether the target noun had a positive or negative valence. The combination of these three words could either be contextually consistent (e.g. ‘very bad - murder’) or inconsistent (e.g. ‘not bad - murder’). EEG recordings revealed that grammatical negations could unfold partly unconsciously, as reflected in similar occipito-parietal N400 effects for conscious and unconscious three-word sequences forming inconsistent combinations. However, only conscious word sequences elicited P600 effects, later in time. Overall, these results suggest that multiple unconscious words can be rapidly integrated and that an unconscious negation can automatically ‘flip the sign’ of an unconscious adjective. These findings not only extend the limits of subliminal combinatorial language processes, but also highlight how consciousness modulates the grammatical integration of multiple words.     

选择性注意对无意识加工的调节作用及潜在机制

意识和无意识经常被看作是动态转换的一体两面,理解意识与无意识相互转换的认知神经机制是当今科学的重大挑战。注意在这个转换过程中发挥关键作用。但是,过往研究主要关注注意对意识的影响,而注意对无意识过程的影响长久以来被忽略了。一个曾比较流行的观点认为无意识加工过程是自动化的,不受注意的调节。然而,该观点近来被逐渐抛弃。在视觉传递通路中,注意可以调节源眼信息、朝向信息的无意识加工过程;在语义系统中,注意能自上而下地增强目标关联性强的,并抑制目标关联性弱的无意识语义过程;在情绪系统中,除了目标关联性之外,由注意负荷操纵的注意供给水平也能调节意识下的情绪加工过程。这些研究有助于更充分理解注意与意识的关系。综合来看,注意既可能是产生意识的必要条件,也可能是（某些）无意识加工的必要条件。未来应深入研究注意调节无意识过程的认知和神经机制,尤其是这些机制在不同注意类型和不同感觉通道间的共性和个性。     

Self-awareness in dreaming.

The process by which self-awareness or subjective experience (consciousness) is maintained has been conceptually and phenomenologically associated primarily with the waking state. In the present study the authors investigate, through introspective reports, the existence and variety of self-awareness in dreaming and whether this phenomenon could, under certain conditions, be distinguished into primary and reflective consciousness. For consistency with theory and dreaming research, instead of reflective consciousness we used the term 'reflective awareness.' Findings indicate that self-awareness in dreaming can be found in its both primary and reflective modes. Phenomenologically, primary consciousness exists in four basic modalities: perceptual, experiential, cognitive, and memory-based recognition. Expressions of these primary consciousness modalities are accessible through introspective interviews during waking. Based on participants' statements, reflective consciousness (awareness) in dreaming was initiated by noticing positive and negative feelings and by personally defined oddities. These findings point to a possible oscillation between primary and reflective consciousness in dreaming. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can binocular rivalry reveal neural correlates of consciousness?

This essay critically examines the extent to which binocular rivalry can provide important clues about the neural correlates of conscious visual perception. Our ideas are presented within the framework of four questions about the use of rivalry for this purpose: (i) what constitutes an adequate comparison condition for gauging rivalry''s impact on awareness, (ii) how can one distinguish abolished awareness from inattention, (iii) when one obtains unequivocal evidence for a causal link between a fluctuating measure of neural activity and fluctuating perceptual states during rivalry, will it generalize to other stimulus conditions and perceptual phenomena and (iv) does such evidence necessarily indicate that this neural activity constitutes a neural correlate of consciousness? While arriving at sceptical answers to these four questions, the essay nonetheless offers some ideas about how a more nuanced utilization of binocular rivalry may still provide fundamental insights about neural dynamics, and glimpses of at least some of the ingredients comprising neural correlates of consciousness, including those involved in perceptual decision-making.     

Cortical processing and perceived timing

As of yet, it is unclear how we determine relative perceived timing. One controversial suggestion is that timing perception might be related to when analyses are completed in the cortex of the brain. An alternate proposal suggests that perceived timing is instead related to the point in time at which cortical analyses commence. Accordingly, timing illusions should not occur owing to cortical analyses, but they could occur if there were differential delays between signals reaching cortex. Resolution of this controversy therefore requires that the contributions of cortical processing be isolated from the influence of subcortical activity. Here, we have done this by using binocular disparity changes, which are known to be detected via analyses that originate in cortex. We find that observers require longer stimulus exposures to detect small, relative to larger, disparity changes; observers are slower to react to smaller disparity changes and observers misperceive smaller disparity changes as being perceptually delayed. Interestingly, disparity magnitude influenced perceived timing more dramatically than it did stimulus change detection. Our data therefore suggest that perceived timing is both influenced by cortical processing and is shaped by sensory analyses subsequent to those that are minimally necessary for stimulus change perception.     

A model of subjective report and objective discrimination as categorical decisions in a vast representational space

Subliminal perception studies have shown that one can objectively discriminate a stimulus without subjectively perceiving it. We show how a minimalist framework based on Signal Detection Theory and Bayesian inference can account for this dissociation, by describing subjective and objective tasks with similar decision-theoretic mechanisms. Each of these tasks relies on distinct response classes, and therefore distinct priors and decision boundaries. As a result, they may reach different conclusions. By formalizing, within the same framework, forced-choice discrimination responses, subjective visibility reports and confidence ratings, we show that this decision model suffices to account for several classical characteristics of conscious and unconscious perception. Furthermore, the model provides a set of original predictions on the nonlinear profiles of discrimination performance obtained at various levels of visibility. We successfully test one such prediction in a novel experiment: when varying continuously the degree of perceptual ambiguity between two visual symbols presented at perceptual threshold, identification performance varies quasi-linearly when the stimulus is unseen and in an ‘all-or-none’ manner when it is seen. The present model highlights how conscious and non-conscious decisions may correspond to distinct categorizations of the same stimulus encoded by a high-dimensional neuronal population vector.     

Development of the Concept of ‘Core Resident Species’ for Quality Assurance of an Insect Reserve

Awareness in the eyes of the public is important for involving the wider community in conservation. A dragonfly awareness trail was developed and implemented in the year 2000 at a national botanical garden in South Africa. Such a trail is not likely to always have the same number of dragonfly species either throughout the year or from one year to the next. The aim was to assess dragonfly assemblage changes that occurred along the trail over 3 years, so as to fine-tune expectations that the public may have as regards species to be seen at any particular time. A cumulative species variance for species and speciesenvironmental relations, strongly indicated that certain measured site variables were responsible for the main variation in dragonfly species patterns over time. Habitat requirements of an odonate species may be defined primarily in terms of marginal grasses, floating and submerged vegetation, marginal herbs, sedges and reeds, and pH. Additional variables were percentage shade, exposed rock, marginal forest and water flow characteristics. Both dragonfly species richness and abundance changed over the 3 years. One of the reasons for this was a single, major disturbance, in the form of dredging the reservoir site to reverse ecological succession in 2002. Despite an impact such as this, and after accounting for vagrancy, there were in all 24 ‘core resident species’ still to be seen along the trail from January to May. Another 11 species, including two migrants and one species lost temporarily to dredging disturbance, can be considered only as ‘possibilities’ on any one visit. Assurance that the 24 core species can be seen in the summer months (although only three in winter) is essential for maintaining the bona fide of such a trail, and hence conservation awareness, in the eyes of the public.     

Neural correlates of the contents of visual awareness in humans

The immediacy and directness of our subjective visual experience belies the complexity of the neural mechanisms involved, which remain incompletely understood. This review focuses on how the subjective contents of human visual awareness are encoded in neural activity. Empirical evidence to date suggests that no single brain area is both necessary and sufficient for consciousness. Instead, necessary and sufficient conditions appear to involve both activation of a distributed representation of the visual scene in primary visual cortex and ventral visual areas, plus parietal and frontal activity. The key empirical focus is now on characterizing qualitative differences in the type of neural activity in these areas underlying conscious and unconscious processing. To this end, recent progress in developing novel approaches to accurately decoding the contents of consciousness from brief samples of neural activity show great promise.     

Social orienting in gaze leading: a mechanism for shared attention

Here, we report a novel social orienting response that occurs after viewing averted gaze. We show, in three experiments, that when a person looks from one location to an object, attention then shifts towards the face of an individual who has subsequently followed the person''s gaze to that same object. That is, contrary to ‘gaze following’, attention instead orients in the opposite direction to observed gaze and towards the gazing face. The magnitude of attentional orienting towards a face that ‘follows’ the participant''s gaze is also associated with self-reported autism-like traits. We propose that this gaze leading phenomenon implies the existence of a mechanism in the human social cognitive system for detecting when one''s gaze has been followed, in order to establish ‘shared attention’ and maintain the ongoing interaction.     

音乐训练影响儿童语音意识的认知神经机制

音乐是一种听觉艺术形式,在儿童教育和发展中,尤其是语言能力发展中扮演着重要角色。语音意识是个体感知识别、分析和运用语音的能力,是预测儿童语言读写能力的重要指标。本文梳理了近十年来音乐训练影响儿童语音意识的研究证据,并讨论了音乐训练可能促进语音意识的神经基础和解释模型。大量研究表明,音乐训练可以在行为水平提高儿童在语音意识测量任务上的成绩。此外,音乐训练从两方面影响语音加工的神经基础：一方面通过影响皮层下基本听觉神经通路与大脑听觉皮层,促进儿童前注意水平的语音感知能力;另一方面通过影响语音加工大脑区域间的功能连接,促进语音编码,强化语音加工的听觉-运动整合功能。相关神经机制为音乐训练促进儿童的语音意识提供了生物学基础。基于已有研究,本文提出综合的层级模型对音乐训练影响儿童语音意识的认知神经机制进行系统的解释,该模型认为音乐训练影响语音意识的认知神经机制分为3个层级：第一层级,音乐训练通过影响基本听觉神经通路促进了语音的基本听觉加工,其中节奏训练促进对语音时长信息的感知,音高训练促进对语音频率信息的感知;第二层级,音乐训练通过影响语音加工的神经网络,进一步促进语音编码,其中节奏训练主要促进...     

The graded and dichotomous nature of visual awareness

Is our visual experience of the world graded or dichotomous? Opposite pre-theoretical intuitions apply in different cases. For instance, when looking at a scene, one has a distinct sense that our experience has a graded character: one cannot say that there is no experience of contents that fall outside the focus of attention, but one cannot say that there is full awareness of such contents either. By contrast, when performing a visual detection task, our sense of having perceived the stimulus or not exhibits a more dichotomous character. Such issues have recently been the object of intense debate because different theoretical frameworks make different predictions about the graded versus dichotomous character of consciousness. Here, we review both relevant empirical findings as well as the associated theories (i.e. local recurrent processing versus global neural workspace theory). Next, we attempt to reconcile such contradictory theories by suggesting that level of processing is an often-ignored but highly relevant dimension through which we can cast a novel look at existing empirical findings. Thus, using a range of different stimuli, tasks and subjective scales, we show that processing low-level, non-semantic content results in graded visual experience, whereas processing high-level semantic content is experienced in a more dichotomous manner. We close by comparing our perspective with existing proposals, focusing in particular on the partial awareness hypothesis.     

An active role of inferior frontal cortex in conscious experience

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Patchwork, Pastoralists, and Perception: Dune Sand as a Valued Resource Among Herders of Inner Mongolia

Scholars have rarely reflected upon dune sand in any context other than that of environmental hazard. Yet recent anthropological research conducted among ethnic Mongol herders in the Keerqin Sandy Lands of Northeast China indicates that native inhabitants exhibit a surprising degree of tolerance, appreciation, and even preference for dune sand at specific spatio-temporal scales. Survey data, gathered primarily through the use of photographic prompts and pile sort exercises during household interviews, reveal that many residents even regard dune sand as the constituent element of a distinctive home environment and cherished way of life. This research underscores the relevance of perception to the policies and practices of human resource management. It also calls into question the authority with which officials and scholars in China and elsewhere indiscriminantly depreciate the various social utilities of dune sand in stock-herding populations.