This article describes human binocular vision. While it is focused primarily on human stereopsis, it also briefly tells about other binocular functions, including binocular summation, rivalry, and vergence, the eye movement that is driven by stereopsis. Stereopsis refers to the depth perception generated by small differences in the locations of visual features in the two retinal images; these differences in retinal location are called disparities. Disparities are detected by special binocularly driven cortical neurons whose properties are outlined here; the article also describes studies that have used fMRI imaging to show that many areas of human cortex respond to depth based on disparity. The development of stereopsis in human infants, as well as clinical abnormalities in stereopsis, is also documented.
Article
Binocular Vision
Suzanne McKee and Preeti Verghese
Article
Brain Basis of Blindsight
Holly Bridge
The sensation of vision arises from the detection of photons of light at the eye, but in order to produce the percept of the world, extensive regions of the brain are required to process the visual information. The majority of information entering the brain via the optic nerve from the eye projects via the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex, the largest visual area, having been reorganized such that one side of the brain represents one side of the world.
Damage to the primary visual cortex in one hemisphere therefore leads to a loss of conscious vision on the opposite side of the world, known as hemianopia. Despite this cortical blindness, many patients are still able to detect visual stimuli that are presented in the blind region if forced to guess whether a stimulus is present or absent. This is known as “blindsight.” For patients to gain any information (conscious or unconscious) about the visual world, the input from the eye must be processed by the brain. Indeed, there is considerable evidence from functional brain imaging that several visual areas continue to respond to visual stimuli presented within the blind region, even when the patient is unaware of the stimulus. Furthermore, the use of diffusion imaging allows the microstructure of white matter pathways within the visual system to be examined to see whether they are damaged or intact. By comparing patients who have hemianopia with and without blindsight it is possible to determine the pathways that are linked to blindsight function. Through understanding the brain areas and pathways that underlie blindsight in humans and non-human primates, the aim is to use modern neuroscience to guide rehabilitation programs for use after stroke.
Article
Dyslexia
Linda Siegel
Dyslexia, or a reading disability, occurs when an individual has great difficulty at the level of word reading and decoding. Comprehension of text, writing, and spelling are also affected. The diagnosis of dyslexia involves the use of reading tests, but the continuum of reading performance means that any cutoff point is arbitrary. The IQ score does not play a role in the diagnosis of dyslexia. Dyslexia is a language-based learning disability. The cognitive difficulties of dyslexics include problems with recognizing and manipulating the basic sounds in a language, language memory, and learning the sounds of letters. Dyslexia is a neurological condition with a genetic basis. There are abnormalities in the brains of dyslexic individuals. There are also differences in the electrophysiological and structural characteristics of the brains of dyslexics. Hope for dyslexia involves early detection and intervention and evidence-based instruction.
Article
Effects of Early Visual Deprivation
Brigitte Röder and Ramesh Kekunnaya
As a consequence of congenital blindness, compensatory performance in the intact sensory modalities has been documented in humans in many domains, including auditory and tactile perception, auditory localization, voice and language processing, and memory. Both changes of the neural circuits associated with the intact sensory systems (intramodal plasticity) and an activation of deprived visual cortex (crossmodal plasticity) have been observed in blind humans. Compensation in congenitally blind and late-blind individuals involves partially different neural mechanisms. If sight is restored in patients who were born with dense bilateral cataracts (opaque lenses preventing patterned light to reach the retina), considerable visual recovery has been observed in basic visual functions even after long periods of visual deprivation. Functional recovery has been found to be lower for higher-order visual processes, which has been linked to deficits in the functional specialization of neural circuits. First evidence has suggested that crossmodal plasticity largely retracts after sight restoration but that crossmodal activity does not seem to fully dissolve. In contrast, intramodal adaptations in the auditory system have been observed to persist after sight restoration. Except for predominantly subcortically mediated multisensory functions, many multisensory processes have been found to be altered even many years after sight restoration.
On the one hand, research in permanently blind humans has documented a high capability of the human neurocognitive system to adapt to an atypical environment. On the other hand, research in sight recovery individuals who had suffered a transient phase of visual deprivation following birth has demonstrated functional specific sensitive periods in the development of visual and multisensory neural circuits.
Article
Enduring Debates on Psychology and Language in the 20th Century
Trevor A. Harley
Research in the psychology of language has been dogged by some enduring controversies, many of which continue to divide researchers. Furthermore, language research has been riven by too many dichotomies and too many people taking too extreme a position, and progress is only likely to be made when researchers recognize that language is a complex system where simple dichotomies may not be relevant. The enduring controversies cover the width of psycholinguistics, including the work of Chomsky and the nature of language, to what extent language is innately determined and the origin of language and how it evolved. Chomsky’s work has also influenced our conceptions of the modularity of the structure of the mind and the nature of psychological processing. Advances in the sophistication of brain imaging techniques have led to debate about exactly what these techniques can tell us about the psychological processing of language. There has also been much debate about whether psychological processing occurs through explicit rules or statistical mapping, a debate driven by connectionist modeling, deep learning, and techniques for the analysis of “big data.” Another debate concerns the role of prediction in language and cognition and the related issues of the relationship between language comprehension and language production. To what extent is language processing embodied, and how does it relate to controversies about “embedded cognition”? Finally, there has been debate about the purpose and use of language.
Article
Hunger
Neil E. Rowland
Hunger is a specific and compelling sensation, sometimes arising from internal signals of nutrient depletion but more often modulated by numerous environmental variables including taste or palatability and ease or cost of procurement. Hunger motivates appetitive or foraging behaviors to find food followed by appropriate proximate or consummatory behaviors to eat it. A critical concept underlying food intake is the flux of chemical energy through an organism. This starts with inputs of food with particular energy content, storage of excess energy as adipose tissue or glycogen, and finally energy expenditure as resting metabolic rate (RMR) or as metabolic rate is modified by physical activity. These concepts are relevant within the context of adequate theoretical accounts based in energy homeostasis; historically, these are mainly static models, although it is now clear that these do not address practical issues such as weight gain through life. Eating is essentially an episodic behavior, often clustered as meals, and this has led to the idea that the meal is a central theoretical concept, but demonstrations that meal patterns are greatly influenced by the environment present a challenge to this tenet. Patterns of eating acquired during infancy and early life may also play a role in establishing adult norms. Direct controls of feeding are those that emphasize food itself as generating internal signals to modify or terminate an ongoing bout of eating, and include a variety of enteroendocrine hormones and brainstem mechanisms. Additionally, many studies point to the essential rewarding or hedonic aspects of food intake, including palatability, and this may involve integrative mechanisms in the forebrain and cerebral cortex.
Article
Kindling
G. Campbell Teskey
The kindling phenomenon is a form of sensitization where, with repetition, epileptiform discharges become progressively longer and behavioral seizures eventually appear and then become more severe. The classic or exogenous kindling technique involves the repeated application of a convulsant stimulus. This technique also lowers seizure thresholds, the minimum intensity of a stimulus required to evoke an electrographic seizure, a process known as epileptogenesis. Endogenous kindling typically occurs following a brain-damaging event which lowers seizure thresholds to the point where self-generated epileptiform discharges recur, lengthen, propagate, and drive progressively more severe behavioral seizures. While exogenous kindling results in alterations in neuronal molecular, cellular/synaptic, and network function that give rise to altered behavior, there is a paucity of evidence for loss of neurons. In contrast, brain-damaging events, with neuronal loss, typically give rise to endogenous kindling. Kindling is a pan-species phenomenon and all mammals that have been examined, including humans, manifest exogenous kindling when seizure-genic (forebrain) structures have been targeted. Since humans display both exogenous and endogenous kindling phenomena this serves as a sober warning to clinicians to prevent seizures. Kindling serves as a robust and reliable model for epileptogenesis, focal as well as secondarily generalized seizures, and certain epileptic disorders.
Article
Lateralization of Brain Function
Lesley J. Rogers
The left and right hemispheres of the brain process sensory information in different ways and function differently in controlling behavior. This lateralization of brain function, originally thought to be unique to humans, is now known to occur in a broad range of non-human vertebrates and even in invertebrates, indicating that it is an essential feature of both large and small brains. Some evidence indicates that lateralization of brain function improves cognitive capacity of the brain. Many, often unrelated, brain functions are lateralized. In humans, these include differential specialization of the hemispheres to process language and produce speech, express emotions, respond to faces, attend to spatial information, and control hand use. As now clear for handedness, both genetic expression and environmental influences are involved in complex ways. Since lateral division of function in the brains of non-human animals has sufficient similarity to that of humans, it is probable that at least some asymmetries were evolutionary precursors to language and speech.
It is notable that lateralization is in no species totally in a single direction. Some evidence from studies of animal species provides support for the hypothesis that alignment of laterality in most individuals in a species occurs only for control of behavior that requires one lateralized individual to interact with another lateralized individual (i.e., in social interaction). In humans, individuals with non-right-handedness (left-handed and mixed-handed) are more prone to a number of psychiatric conditions or other behavioral conditions, including autism, schizophrenia, and dyslexia.
Article
Mirror Neurons, Empathy, and the Other
Marco Iacoboni
Empathy is the ability to understand and share the feelings of other people. It extends also to the ability to understand and share the feelings of animals and fictional characters. Empathy is essential to properly function in social interactions. It is also typically higher for people who belong to one’s own social group and lower for people who belong to a different social group. Lack of empathy is associated with severe mental health conditions including psychopathy, narcissism, and antisocial personality disorder.
Empathy is a complex, flexible, adaptive, and nuanced function for navigating social settings that involves the interplay of multiple neural systems. A crucial neural system for empathy is the mirror neuron system, formed by cells with a variety of properties and the shared feature of being activated during the actions of the self and the perception of actions of other people. The mirroring of the actions of other people in one’s brain allows an understanding from within of the other’s intentions, motivation, and feelings.
Article
Music Perception
Marcus T. Pearce
Music perception covers all aspects of psychological and neural processing invoked while listening to music. In order to make sense of a musical stimulus, the perceptual system must infer an internal representation of the structure present in a piece of music, including the attributes of individual events (including pitch, timbre, loudness, and timing), groups of events (such as chords, voices, and phrases), and structural relationships between such groups, so that larger-scale aspects of musical form and thematic structure can be perceived. Such representations are stored in memory at timescales ranging from seconds for echoic memory to decades in the case of long-term memory for music, which consists of schematic knowledge of musical styles, veridical memory for particular familiar pieces of music, and episodic memory for music heard at a particular place and time. Stored representations of music allow the generation of top-down expectations for the attributes of forthcoming events while listening to music, which play a role in the perception of music as it unfolds dynamically in time and also the emotional and aesthetic experience of music. Music is a communicative medium conveying affective meaning from the composer and performer to the listener, via several psychological mechanisms and using a range of cues in the music, some of which are universal, others culture-specific. Individuals show behavioral and physiological effects of listening to music from birth onward and learn the syntactic structure of the musical styles to which they are exposed within their culture, shaping their music perception. Some individuals undertake explicit musical training, which can additionally shape their perception of music, sometimes in fundamental ways. Listening to music can impair performance on concurrent tasks involving working memory due to competing access for resources but can improve performance when listening takes place prior to the task due to its positive effect on affective state. Music is a universal human cultural phenomenon whose complexity requires the activation of a diverse range of perceptual and cognitive mechanisms, making it an interesting target for psychological and neuroscientific investigation.
Article
Neurocognitive Aging and Functional Connectivity Using Functional Magnetic Resonance Imaging
Hana Burianová
Determining the mechanisms that underlie neurocognitive aging, such as compensation or dedifferentiation, and facilitating the development of effective strategies for cognitive improvement is essential due to the steadily rising aging population. One approach to study the characteristics of healthy aging comprises the assessment of functional connectivity, delineating markers of age-related neurocognitive plasticity. Functional connectivity paradigms characterize complex one-to-many (or many-to-many) structure–function relations, as higher-level cognitive processes are mediated by the interaction among a number of functionally related neural areas rather than localized to discrete brain regions. Task-related or resting-state interregional correlations of brain activity have been used as reliable indices of functional connectivity, delineating age-related alterations in a number of large-scale brain networks, which subserve attention, working memory, episodic retrieval, and task-switching. Together with behavioral and regional activation studies, connectivity studies and modeling approaches have contributed to our understanding of the mechanisms of age-related reorganization of distributed functional networks; specifically, reduced neural specificity (dedifferentiation) and associated impairment in inhibitory control and compensatory neural recruitment.
Article
Physical Activity and Inactivity Impacts on Cognitive and Emotional Functioning in Later Life
Patrick D. Gajewski and Michael Falkenstein
Healthy aging is associated with changes in sensory, motor, cognitive, and emotional functions. Such changes depend on various factors. In particular, physical activity not only improves physical and motor but also cognitive and emotional functions. Observational (i.e., associations) and cross-sectional studies generally show a positive effect of regular physical exercise on cognition in older adults. Most longitudinal randomized controlled intervention studies also show positive effects, but the results are inconsistent due to large heterogeneity of methodological setups. Positive changes accompanying physical activity mainly impact executive functions, memory functions, and processing speed. Several factors influence the impact of physical activity on cognition, mainly the type and format of the activity. Strength training and aerobic training yield comparable but also differential benefits, and all should be used in physical activities. Also, a combination of physical activity with cognitive activity appears to enhance its effect on cognition in older age. Hence, such combined training approaches are preferable to homogeneous trainings. Studies of brain physiology changes due to physical activity show general as well as specific effects on certain brain structures and functions, particularly in the frontal cortex and the hippocampus, which are those areas most affected by advanced age. Physical activity also appears to improve cognition in patients with mild cognitive dysfunction and dementia and often ameliorates the disease symptoms. This makes physical training an important intervention for those groups of older people.
Apart from cognition, physical activity leads to improvement of emotional functions. Exercise can lead to improvement of psychological well-being in older adults. Most importantly, exercise appears to reduce symptoms of depression in seniors. In future intervention studies it should be clarified who profits most from physical activity. Further, the conditions that influence the cognitive and emotional benefits older people derive from physical activity should be investigated in more detail. Finally, measures of brain activity that can be easily applied should be included as far as possible.
Article
Thirst
Neil E. Rowland
Thirst is a specific and compelling sensation, often arising from internal signals of dehydration but modulated by many environmental variables. There are several historical landmarks in the study of thirst and drinking behavior. The basic physiology of body fluid balance is important, in particular the mechanisms that conserve fluid loss. The transduction of fluid deficits can be discussed in relation to osmotic pressure (osmoreceptors) and volume (baroreceptors). Other relevant issues include the neurobiological mechanisms by which these signals are transformed to intracellular and extracellular dehydration thirsts, respectively, including the prominent role of structures along the lamina terminalis. Other considerations are the integration of signals from natural dehydration conditions, including water deprivation, thermoregulatory fluid loss, and thirst associated with eating dry food. These mechanisms should also be considered within a broader theoretical framework of organization of motivated behavior based on incentive salience.
