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Biological Basis of Behavior
Published in Mohamed Ahmed Abd El-Hay, Understanding Psychology for Medicine and Nursing, 2019
The occipital cortex is the smallest of the four lobes of the brain. It is located posterior to the temporal lobe and parietal lobes. The occipital cortex is concerned with visual processing and is composed of primary visual cortex (Brodmann area 17), and secondary visual (association) cortex (Brodmann areas 18 and 19). It receives projections from the retina (via the thalamus) from where different groups of neurons separately encode different visual information, such as color, orientation, and motion. Two important pathways of information originate in the occipital lobes: the dorsal and ventral streams. The dorsal stream projects to the parietal lobes and processes where objects are located. The ventral stream projects to structures in the temporal lobes and processes what objects are.
Vision and Higher Cortical Function
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
Sonia Gill, John Ulmer, Edgar A. DeYoe
At the coarsest anatomical scale, occipital visual areas and pathways can be grouped rather loosely into two major streams, the dorsal stream extending from VI into parietal cortex and the ventral stream extending from VI into inferotemporal cortex (Fig. 4). There is a tendency for lesions of the dorsal stream to disrupt visual tasks involving guidance of actions directed toward objects within the visual field, whereas lesions of the ventral stream tend to disrupt identification tasks (11–13). Consequently, the two paths have been dubbed the “where” versus “what” systems, though this by no means captures their true functional complexity. Indeed, it has been proposed that operation of the dorsal stream to guide actions can occur without eliciting visual awareness whereas operation of the ventral stream may itself lead to visual awareness and memory (13). At a finer scale, individual visual areas in the human have been defined in part by retinotopy (see above) and in part by functional distinctions established by lesion effects or neuroimaging. The exact boundaries of many visual areas are difficult to identify precisely and in many instances remain open to future modification.
Varieties of learning and developmental theories of memory
Published in Romain Meeusen, Sabine Schaefer, Phillip Tomporowski, Richard Bailey, Physical Activity and Educational Achievement, 2017
Phillip Tomporowski, Daniel M. Pendleton, Bryan A. McCullick
Central to perceptual learning is the capacity to capture and recognize events as they occur. At a fundamental level, humans learn about the world they live in based on the experiences they derived from the stimulation of the sensory systems. Consider, for instance, how one can pick out the face of a friend in a crowded room. As the features of every person’s face are unique, they reflect a specific array of light waves that enter the eyes and stimulate photoreceptors on the retina that, in turn, send neural transmissions through the lateral geniculate of the thalamus and on to the striate cortex and the primary visual cortex. There the attributes of the incoming information flow are analysed in terms of form, colour and movement. Information then separates into two streams: the ventral stream flows towards the inferior temporal lobe and is used to recognize the visual experience; the dorsal stream flows toward the posterior parietal cortex and provides information concerning the location of what is seen. Together, the two streams provide the basis for our ability to recognize objects and their locations.
Posterior cortical atrophy: clinical, neuroimaging, and neuropathological features
Published in Expert Review of Neurotherapeutics, 2023
John Best, Marianne Chapleau, Gil D. Rabinovici
Visual processing in the brain follows two distinct anatomical and functional streams – ventral and dorsal [6]. The ventral stream (occipitotemporal), colloquially referred to as the ‘what’ pathway, processes information about an object’s identity characteristics. In contrast, the dorsal stream (temporoparietal), colloquially referred to as the ‘where’ pathway, processes information about an object’s location and thus informs visuomotor control pathways. These frameworks continue to be reshaped, with work by Kravitz et al. proposing numerous subcategories of spatial processing in the dorsal stream [7]. These include distinct networks for eye movements and spatial working memory, visually guided actions, and navigation, with intermediate networks helping to integrate different spatial mental representations. Most patients with PCA present with a mix of dorsal greater than ventral stream involvement, though cases of focal neurodegeneration in the ventral stream have been described [8–10]. Further subclassification of PCA has also highlighted a more rare ‘Primary Occipital Variant’ of PCA. This variant is considered a caudal variant, with deficits, atrophy, and hypometabolism focused primarily in the occipital lobes with relative sparing of parietal lobe structures and bedside testing demonstrating more pronounced primary visual processing deficits (e.g., impaired color perception) [11]. Earliest symptoms can shed some light as to the site of earliest and greatest neurodegeneration.
The effect of mild traumatic brain injury on the visual processing of global form and motion
Published in Brain Injury, 2019
Mohammed M. Alnawmasi, Arijit Chakraborty, Kristine Dalton, Patrick Quaid, Benjamin T. Dunkley, Benjamin Thompson
Ventral and dorsal stream function can be measured psychophysically (31,32). This approach is based on the linking assumption that psychophysical tasks can target brain areas such as V4 in the ventral stream and MT in the dorsal stream. These areas integrate local signals from V1 and V2 into coherent, global representations of form (V4) or motion (MT) (33). Global form tasks designed to measure ventral stream function require the combination of local form cues into a coherent shape or pattern (32,34). Glass patterns, constructed from multiple pairs of dots that can be configured into a coherent pattern, are a common global form stimulus. Similarly, global motion tasks that are used to measure dorsal stream function involve the integration of multiple local motion signals into a coherent motion percept (31,35). Global motion tasks often utilize stimuli constructed from groups of moving dots called random dot kinematograms (RDKs), whereby a sub-set of “signal” dots move coherently in a common direction and the remaining “noise” dots move in random directions. The observer’s task is to identify the direction of coherent motion and the signal to noise ratio in the stimulus is manipulated to determine a motion coherence threshold (31,35,36). Measurements of basic visual functions such as spatial or temporal contrast sensitivity can be used to assess whether deficits in global processing tasks are due to abnormal integration of local signals or impairments in the early-stage (pre-integration) processing of visual information (36,37).
Attention and visuo-spatial function in children without cerebral palsy who were cooled for neonatal encephalopathy: a case-control study
Published in Brain Injury, 2019
James Tonks, Grace Cloke, Richard Lee-Kelland, Sally Jary, Marianne Thoresen, Frances M Cowan, Ela Chakkarapani
One theory of relevance in understanding how NE may affect attention and visuo-spatial functions is the Dorsal Stream Vulnerability model (11,12). Visual processing is divided into two specialized extra-striate streams; a ventral stream, or ‘what’ stream projecting from the visual cortex to temporal lobe structures, which is integral to object processing; and a dorsal stream, or ‘where’ stream projecting from the visual cortex to the parietal lobe, which is essential in spatial processing (13–15). Selective, rapid visual attention processes in location and movement of objects, and visuo-spatial functions (such as spatial transformation and visuo-spatial relations) are dependent on the “dorsal stream” pathway in the brain (12,16). Previous studies have indicated that abilities that we now associate with dorsal stream function do appear to be affected by perinatal brain injury, and particularly hypoxic-ischemic injury (17,18). It is therefore reasonable to hypothesize that children cooled for NE who do not have problems severe enough to cause CP could still have effects on dorsal stream functions, despite treatment. Children with early (though not neonatal) brain injury commonly have problems with visuo-spatial relations, which often become more apparent at around 10 years (19). That is, visual-spatial tests are sensitive in differentiating between healthy children and children after brain injury. Similar findings have been reported in relation to attention difficulties which can also become more evident from 10 years, with attention-switching skills having some interdependence with later developing executive function (20).