Visual Neuroscience is a branch of

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

that focuses on the visual system of the human body, mainly located in the brain's

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

. The main goal of visual neuroscience is to understand how neural activity results in

visual perception Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflecte ...

, as well as behaviors dependent on vision. In the past, visual neuroscience has focused primarily on how the brain (and in particular the

Visual Cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

) responds to light rays projected from static images and onto the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

. While this provides a reasonable explanation for the

of a static image, it does not provide an accurate explanation for how we perceive the world as it really is, an ever-changing, and ever-moving 3-D environment. The topics summarized below are representative of this area, but far from exhaustive. To be less topic specific, one can see this textbook for the computational link between neural activities and visual perception and behavior: "Understanding vision: theory, models, and data" , published by Oxford University Press 2014.

Face processing

A recent study using

Event-Related Potentials An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus. The study of the brain ...

( ERPs) linked an increased neural activity in the occipito-temporal region of the brain to the visual categorization of facial expressions. Results focus on a negative peak in the ERP that occurs 170 milliseconds after the stimulus onset. This

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

, called the

N170 The N170 is a component of the event-related potential (ERP) that reflects the neural processing of faces, familiar objects or words. Furthermore, the N170 is modulated by prediction error processes. When potentials evoked by images of faces are co ...

, was measured using electrodes in the occipito-temporal region, an area already known to be changed by face stimuli. Studying by using the

EEG Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

, and ERP methods allow for an extremely high

temporal resolution Temporal resolution (TR) refers to the discrete resolution of a measurement with respect to time. Physics Often there is a trade-off between the temporal resolution of a measurement and its spatial resolution, due to Heisenberg's uncertainty pri ...

of 4 milliseconds, which makes these kinds of experiments extremely well suited for accurately estimating and comparing the time it takes the brain to perform a certain function. Scientists used classification image techniques, to determine what parts of complex visual stimuli (such as a face) will be relied on when patients are asked to assign them to a category, or

emotion Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...

. They computed the important features when the stimulus face exhibited one of five different emotions. Stimulus faces exhibiting fear had the distinguishing feature of widening eyes, and stimuli exhibiting happiness exhibited a change in the mouth to make a smile. Regardless of the expression of the stimuli's face, the region near the eyes affected the

before the regions near the mouth. This revealed a sequential, and predetermined order to the

perception Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...

and processing of faces, with the eye being the first, and the mouth, and nose being processed after. This process of downward integration only occurred when the inferior facial features were crucial to the categorization of the stimuli. This is best explained by comparing what happens when participants were shown a face exhibiting fear, versus happiness. The

peaked slightly earlier for the fear stimuli at about 175 milliseconds, meaning that it took a participants less time to recognize the facial expression. This is expected because only the eyes need to be processed to recognize the emotion. However, when processing a happy expression, where the mouth is crucial to categorization, downward integration must take place, and thus the

peak occurred later at around 185 milliseconds. Eventually visual neuroscience aims to completely explain how the

visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the a ...

processes all changes in faces as well as objects. This will give a complete view to how the world is constantly visually perceived, and may provide insight into a link between

and

consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...

Perceptions of light and shadows

Recently, scientists have conducted experiments challenging the hierarchal process of

of lightness. These experiments have suggested that the perception of lightness is derived from a much higher level of

cognition Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...

involving the interpretation of illuminations and

shadows A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, o ...

rather than the process occurring at a basic single unit level. This idea is best explained by examining two different versions of two common visual illustrations. The first set of illustrations cause a

phenomenon A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfried W ...

known as the induction effect. The image consists of two identical gray squares, surrounded by black and white respectively. The result is that the perception of the gray on the white is darker than the gray on the black. The traditional way of explaining this is through

lateral inhibition In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction ...

. A cell with a receptive field in the gray square surrounded by the white receives more of the

and thus it does not fire as often and appears darker. The second set of illustrations explain the Craik-O'Brien-Cornsweet illusion. This includes a sharp transition from black to white in the middle then fading to medium gray on the other side. The other two diagrams exhibit the same two effects but with a much greater

intensity Intensity may refer to: In colloquial use *Strength (disambiguation) *Amplitude * Level (disambiguation) * Magnitude (disambiguation) In physical sciences Physics *Intensity (physics), power per unit area (W/m2) *Field strength of electric, ma ...

. This is due to the shapes in the illustrations being 3-dimensional causing the human mind to interpret the seemingly darker areas as shadows. This was first introduced by

Ernst Mach Ernst Waldfried Josef Wenzel Mach ( , ; 18 February 1838 – 19 February 1916) was a Moravian-born Austrian physicist and philosopher, who contributed to the physics of shock waves. The ratio of one's speed to that of sound is named the Mach ...

in 1866.

Visual neuroscience and clinical neuropsychology

The continuous research into visual neuroscience has resulted in an ever-growing knowledge of the human

. It has filled in many of the steps between the moment when light hits our

to when we experience

of our world.

Insight Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings: *a piece of information *the act or result of understanding the inner nature of things or of seeing intu ...

into this process allows

clinical psychologists Clinical psychology is an integration of social science, theory, and clinical knowledge for the purpose of understanding, preventing, and relieving psychologically based distress or dysfunction and to promote subjective well-being and personal ...

to gain a greater understanding for what may be causing visual disorders in their patients. While understanding the underlying process of a visual disorder alone will not provide a patient with treatment, it will put both the patient and the

clinician A clinician is a health care professional typically employed at a skilled nursing facility or clinic. Clinicians work directly with patients rather than in a laboratory or as a researcher. A clinician may diagnose, treat, and otherwise care for pa ...

at ease knowing exactly what they are dealing with from a scientific perspective rooted in visual neuroscience research rather than a descriptive account of

symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an disease, illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormali ...

by the patient.

References

{{Reflist, refs= Schwartz, S. H. (2010). Visual Perception a clinical orientation(fourth edition). New York: The McGraw-Hill Companies. Eimer, M., and Holmes, A. (2007). Event-related brain potential correlates of emotional face processing.

Neuropsychologia ''Neuropsychologia'' is a peer-reviewed scientific journal that focuses on cognitive neuroscience. It was established in 1963, and is published by Elsevier (formerly Pergamon Press Pergamon Press was an Oxford-based publishing house, founded ...

45, 15–31. Gosselin, F., and Schyns, P.G. (2001). Bubbles: a technique to reveal the use of information in recognition tasks. Vision Res. 41, 2261–2271. Rainer, G. (2008). Visual neuroscience: computational brain dynamics of face processing.

Current Biology ''Current Biology'' is a biweekly peer-reviewed scientific journal that covers all areas of biology, especially molecular biology, cell biology, genetics, neurobiology, ecology, and evolutionary biology. The journal includes research articles, var ...

, 17(21), R933-R934. Schyns, P.G., Petro, L.S., and Smith, M.L. (2007). Dynamics of visual information integration in the brain to categorize facial expressions.

17, 1580–1585. Paradiso, M. (2000). Visual Neuroscience: illuminating the dark corners.

10(1), R15–R18. Logvinenko AD: Lightness induction revisited. Perception 1999, 28:803-816. Vuilleumier, P., & Pourtois, G. (2007). Distributed and interactive brain mechanisms during emotion face perception: evidence from functional neuroimaging.

45, 174–194. Zhaoping, L. (2014). Understanding vision: theory, models, and data. Oxford University Press. Neuroscience Visual perception