Descartes on the Cognitive Structure of Sensory Experience

Descartes is often thought to bifurcate sensory experience into two distinct cognitive components: the sensing of secondary qualities and the more or less intellectual perceiving of primary qualities. A closer examination of his analysis of sensory perception in the Sixth Replies and his treatment of sensory processing in the Dioptrics and Treatise on Man tells a different story. I argue that Descartes offers a unified cognitive account of sensory experience according to which the senses and intellect operate together to produce a fundamentally imagistic representation of the world in both its primary and secondary quality aspects. At stake here is not only our understanding of the cognitive structure of sensory experience but the relation of sense and intellect more generally in the Cartesian mind. The deep bifurcation in the Cartesian mind is not between the sensory perception of primary and secondary qualities but between sensory perception and purely intellectual perception.     

Differential activation patterns of occipital and prefrontal cortices during motion processing: Evidence from normal and schizophrenic brains

Visual motion perception is normally mediated by neural processing in the posterior cortex. Focal damage to the middle temporal area (MT), a posterior extrastriate region, induces motion perception impairment. It is unclear, however, how more broadly distributed cortical dysfunction affects this visual behavior and its neural substrates. Schizophrenia manifests itself in a variety of behavioral and perceptual abnormalities that have proved difficult to understand through a dysfunction of any single brain system. One of these perceptual abnormalities involves impaired motion perception. Motion processing provides an opportunity to clarify the roles of multiple cortical networks in both healthy and schizophrenic brains. Using fMRI, we measured cortical activation while participants performed two visual motion tasks (direction discrimination and speed discrimination) and one nonmotion task (contrast discrimination). Normal controls showed robust cortical activation (BOLD signal changes) in MT during the direction and speed discrimination tasks, documenting primary processing of sensory input in this posterior region. In patients with schizophrenia, cortical activation was significantly reduced in MT and significantly increased in the inferior convexity of the prefrontal cortex, an area that is normally involved in higher level cognitive processing. This shift in cortical responses from posterior to prefrontal regions suggests that motion perception in schizophrenia is associated with both deficient sensory processing and compensatory cognitive processing. Furthermore, this result provides evidence that in the context of broadly distributed cortical dysfunction, the usual functional specificity of the cortex becomes modified, even across the domains of sensory and cognitive processing.     

Is neocortex essentially multisensory?

Although sensory perception and neurobiology are traditionally investigated one modality at a time, real world behaviour and perception are driven by the integration of information from multiple sensory sources. Mounting evidence suggests that the neural underpinnings of multisensory integration extend into early sensory processing. This article examines the notion that neocortical operations are essentially multisensory. We first review what is known about multisensory processing in higher-order association cortices and then discuss recent anatomical and physiological findings in presumptive unimodal sensory areas. The pervasiveness of multisensory influences on all levels of cortical processing compels us to reconsider thinking about neural processing in unisensory terms. Indeed, the multisensory nature of most, possibly all, of the neocortex forces us to abandon the notion that the senses ever operate independently during real-world cognition.     

How brains beware: neural mechanisms of emotional attention

Emotional processes not only serve to record the value of sensory events, but also to elicit adaptive responses and modify perception. Recent research using functional brain imaging in human subjects has begun to reveal neural substrates by which sensory processing and attention can be modulated by the affective significance of stimuli. The amygdala plays a crucial role in providing both direct and indirect top-down signals on sensory pathways, which can influence the representation of emotional events, especially when related to threat. These modulatory effects implement specialized mechanisms of 'emotional attention' that might supplement but also compete with other sources of top-down control on perception. This work should help to elucidate the neural processes and temporal dynamics governing the integration of cognitive and affective influences in attention and behaviour.     

Differential effects of stimulus context in sensory processing

Stimulus contexts in which different intensity levels are presented to two sensory–perceptual channels can produce differential effects on perception: Perceived magnitudes are depressed in whichever channel received the stronger stimuli. Context differentially can affect loudness at different sound frequencies or perceived length of lines in different spatial orientations. Reported in hearing, vision, haptic touch, taste, and olfaction, differential context effects (DCEs) are a general property of perceptual processing. Characterizing their functional properties and determining their underlying mechanisms are essential both to fully understanding sensory and perceptual processes and to properly interpreting sensory measurements obtained in applied as well as basic research settings.     

Integrating face and voice in person perception

Integration of information from face and voice plays a central role in our social interactions. It has been mostly studied in the context of audiovisual speech perception: integration of affective or identity information has received comparatively little scientific attention. Here, we review behavioural and neuroimaging studies of face-voice integration in the context of person perception. Clear evidence for interference between facial and vocal information has been observed during affect recognition or identity processing. Integration effects on cerebral activity are apparent both at the level of heteromodal cortical regions of convergence, particularly bilateral posterior superior temporal sulcus (pSTS), and at 'unimodal' levels of sensory processing. Whether the latter reflects feedback mechanisms or direct crosstalk between auditory and visual cortices is as yet unclear.     

The concept of auditory stimulus representation in cognitive neuroscience

The sequence of neurophysiological processes elicited in the auditory system by a sound is analyzed in search of the stage at which the processes carrying sensory information cross the borderline beyond which they directly underlie sound perception. Neurophysiological data suggest that this transition occurs when the sensory input is mapped onto the physiological basis of sensory memory in the auditory cortex. At this point, the sensory information carried by the stimulus-elicited process corresponds, for the first time, to that contained by the actual sound percept. Before this stage, the sensory stimulus code is fragmentary, lacks the time dimension, cannot enter conscious perception, and is not accessible to top-down processes (voluntary mental operations). On these grounds, 2 distinct stages of auditory sensory processing, prerepresentational and representational, can be distinguished.     

Event perception: a mind-brain perspective

People perceive and conceive of activity in terms of discrete events. Here the authors propose a theory according to which the perception of boundaries between events arises from ongoing perceptual processing and regulates attention and memory. Perceptual systems continuously make predictions about what will happen next. When transient errors in predictions arise, an event boundary is perceived. According to the theory, the perception of events depends on both sensory cues and knowledge structures that represent previously learned information about event parts and inferences about actors' goals and plans. Neurological and neurophysiological data suggest that representations of events may be implemented by structures in the lateral prefrontal cortex and that perceptual prediction error is calculated and evaluated by a processing pathway, including the anterior cingulate cortex and subcortical neuromodulatory systems.     

Cerebellar patients demonstrate preserved implicit knowledge of association strengths in musical sequences

Recent findings suggest the involvement of the cerebellum in perceptual and cognitive tasks. Our study investigated whether cerebellar patients show musical priming based on implicit knowledge of tonal-harmonic music. Participants performed speeded phoneme identification on sung target chords, which were either related or less-related to prime contexts in terms of the tonal-harmonic system. As groups, both cerebellar patients and age-matched controls showed facilitated processing for related targets, as previously observed for healthy young adults. The outcome suggests that an intact cerebellum is not mandatory for accessing implicit knowledge stored in long-term memory and for its influence on perception. One patient showed facilitated processing for less-related targets (suggesting sensory priming). The findings suggest directions for future research on auditory perception in cerebellar patients to further our understanding of cerebellar functions.     

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.     

Predictions penetrate perception: Converging insights from brain,behaviour and disorder

It is argued that during ongoing visual perception, the brain is generating top-down predictions to facilitate, guide and constrain the processing of incoming sensory input. Here we demonstrate that these predictions are drawn from a diverse range of cognitive processes, in order to generate the richest and most informative prediction signals. This is consistent with a central role for cognitive penetrability in visual perception. We review behavioural and mechanistic evidence that indicate a wide spectrum of domains—including object recognition, contextual associations, cognitive biases and affective state—that can directly influence visual perception. We combine these insights from the healthy brain with novel observations from neuropsychiatric disorders involving visual hallucinations, which highlight the consequences of imbalance between top-down signals and incoming sensory information. Together, these lines of evidence converge to indicate that predictive penetration, be it cognitive, social or emotional, should be considered a fundamental framework that supports visual perception.     

Behavioral evidence for task-dependent “what” versus “where” processing within and across modalities

Task-dependent information processing for the purpose of recognition or spatial perception is considered a principle common to all the main sensory modalities. Using a dual-task interference paradigm, we investigated the behavioral effects of independent information processing for shape identification and localization of object features within and across vision and touch. In Experiment 1, we established that color and texture processing (i.e., a “what” task) interfered with both visual and haptic shape-matching tasks and that mirror image and rotation matching (i.e., a “where” task) interfered with a feature-location-matching task in both modalities. In contrast, interference was reduced when a “where” interference task was embedded in a “what” primary task and vice versa. In Experiment 2, we replicated this finding within each modality, using the same interference and primary tasks throughout. In Experiment 3, the interference tasks were always conducted in a modality other than the primary task modality. Here, we found that resources for identification and spatial localization are independent of modality. Our findings further suggest that multisensory resources for shape recognition also involve resources for spatial localization. These results extend recent neuropsychological and neuroimaging findings and have important implications for our understanding of high-level information processing across the human sensory systems.     

Behavioral evidence for task-dependent "what" versus "where" processing within and across modalities

Task-dependent information processing for the purpose of recognition or spatial perception is considered a principle common to all the main sensory modalities. Using a dual-task interference paradigm, we investigated the behavioral effects of independent information processing for shape identificationand localization ofobject features within and across vision and touch. In Experiment 1, we established that color and texture processing (i.e., a "what" task) interfered with both visual and haptic shape-matching tasks and that mirror image and rotation matching (i.e., a "where" task) interfered with a feature-location-matching task in both modalities. In contrast, interference was reduced when a "where" interference task was embedded in a "what" primary task and vice versa. In Experiment 2, we replicated this finding within each modality, using the same interference and primary tasks throughout. In Experiment 3, the interference tasks were always conducted in a modality other than the primary task modality. Here, we found that resources for identification and spatial localization are independent of modality. Our findings further suggest that multisensory resources for shape recognition also involve resources for spatial localization. These results extend recent neuropsychological and neuroimaging findings and have important implications for our understanding of high-level information processing across the human sensory systems.     

大脑视知觉调控的神经机制

大脑的知觉加工并非单纯由外部刺激驱动,而是存在自上而下的知觉调控。尽管这一现象被大量实验研究证实,但其神经机制仍然是认知神经科学研究的重要问题。本研究系统介绍了知觉调控的神经基础、实现形式、研究范式,及其理论模型,分析指出了当前研究面临的主要问题,并对未来的研究进行了展望,以期促进该问题研究的进一步开展。     

Language as context for the perception of emotion

In the blink of an eye, people can easily see emotion in another person's face. This fact leads many to assume that emotion perception is given and proceeds independently of conceptual processes such as language. In this paper we suggest otherwise and offer the hypothesis that language functions as a context in emotion perception. We review a variety of evidence consistent with the language-as-context view and then discuss how a linguistically relative approach to emotion perception allows for intriguing and generative questions about the extent to which language shapes the sensory processing involved in seeing emotion in another person's face.     

Components of visual prior entry

The prior entry hypothesis contends that attention accelerates sensory processing, shortening the time to perception. Typical observations supporting the hypothesis may be explained equally well by response biases, changes in decision criteria, or sensory facilitation. In a series of experiments conducted to discriminate among the potential mechanisms, observers judged the simultaneity or temporal order of two stimuli, to one of which attention was oriented by exogenous, endogenous, gaze-directed, or multiple exogenous cues. The results suggest that prior entry effects are primarily caused by sensory facilitation and attentional modifications of the decision mechanism, with only a small part possibly due to an attention-dependent sensory acceleration.     

Tonal expectations influence pitch perception

In this study, we investigated the influence of tonal relatedness on pitch perception in melodies. Tonal expectations for target tones were manipulated in melodic contexts while controlling sensory expectations, thus allowing us to assess specifically the influence oftonal expectations on pitch perception. Three experimentsprovided converging evidence that tonal relatedness modulates pitch perception in nonmusician listeners. Experiment 1 showed, with a rating task, the influence of the tonal relatedness of a target tone on listeners' judgments of tuning/mistuning. Experiment 2 showed, with a priming task, that pitch processing of in-tune tones was faster for tonally related targets than for less related targets. Experiment 3 showed, with a comparison task, that discrimination performance for small mistunings was better when the to-be-compared tones were tonally related to the melodic context. Findings are discussed in relation to psychoacoustic research on contextual pitch perception and to studies showing facilitation of early processing steps via knowledge- and attention-related processes.     

Left-Hemisphere Dominance for Motion Processing in Deaf Signers

Evidence from neurophysiological studies in animals as well as humans has demonstrated robust changes in neural organization and function following early-onset sensory deprivation. Unfortunately, the perceptual consequences of these changes remain largely unexplored. The study of deaf individuals who have been auditorily deprived since birth and who rely on a visual language (i.e., American Sign Language, ASL) for communication affords a unique opportunity to investigate the degree to which perception in the remaining, intact senses (e.g., vision) is modified as a result of altered sensory and language experience. We studied visual motion perception in deaf individuals and compared their performance with that of hearing subjects. Thresholds and reaction times were obtained for a motion discrimination task, in both central and peripheral vision. Although deaf and hearing subjects had comparable absolute scores on this task, a robust and intriguing difference was found regarding relative performance for left-visual-field (LVF) versus right-visual-field (RVF) stimuli: Whereas hearing subjects exhibited a slight LVF advantage, the deaf exhibited a strong RVF advantage. Thus, for deaf subjects, the left hemisphere may be specialized for motion processing. These results suggest that perceptual processes required for the acquisition and comprehension of language (motion processing, in the case of ASL) are recruited (or "captured") by the left, language-dominant hemisphere.     

Levels of processing: a view from functional brain imaging

This paper briefly reviews two central assumptions of the levels-of-processing framework in the light of findings from recent PET and fMRI studies: First, to address the suggestion that memory traces can be seen as records of analyses carried out for the purposes of perception and comprehension, studies on encoding-retrieval overlap in brain activation patterns are considered. Second, to address the suggestion that deeper, more semantic, processing results in more durable traces, studies of how encoding activity relates to processing depth and subsequent memory performance are examined. The results show that some of the sensory regions that are activated during initial perception are subsequently reactivated during retrieval, and activity in frontal and medial-temporal brain regions is related to depth of processing and level of memory performance. Collectively, these results provide support for central components of the levels framework.