Is the understanding that something exists even though it is not in sight or has been removed from the field of vision?

Elementary Aspects of Visual Perception

In visual perception, the recurrence or prolongation of a visual phenomenon beyond the customary limits of the appearance of the real event in the world is termedpalinopsia (Cutting, 1997).Critchley (1951) gave a number of examples: a cat noticed in the street one day kept appearing at various times and various situations over the next few days, and the words ‘Pullman Springs’ noticed on the back of a van kept appearing on other vehicles over the next few months.

The size of the perception can be either larger (macropsia) or smaller (micropsia) than expected. In some cases, there can be apparent reduction in one hemifield of vision (hemimicropsia). These anomalies are common in temporal lobe epilepsy. Alteration in the customary shape of the perceived object is termedmetamorphopsia. Usually, this may involve the appearance of things taking on a different aspect: ‘One woman saw people upside down, on their heads’ (Bleuler, 1950). This is an example of inversion. When metamorphopsia affects faces, it is referred to asparaprosopia. Typically, these perceptual distortions of faces are rapidly fluctuant and dynamic.Schreber (1955) describes his experience as follows: ‘At the same time I repeatedly witnessed that [some patients] changed heads during their stay in the common room; that is to say without leaving the room and while I was observing them, they suddenly ran about with a different head’.Bleuler (1950) also describes, ‘Wardmates change their faces the very moment that one looks at them’. One ofCutting's patients (1997) said, ‘Man behind a lorry was pulling hideous faces’.

Different aspects of colour perception can be affected. The intensity of the colour (visual hyperaesthesia), the actual hue and the quality of the colour can all be affected.Cutting (1997) gives several examples:

‘colours are brighter’, ‘colours more vivid – red, yellow, orange stood out’;

‘black looked brown sometimes’, ‘brown looked different; trouble with pink as it comes across as green’; and

‘this colour looks like an old blue – something horrible’.

Bleuler (1950) describes ‘one patient sees everything as coloured red; another sees everything as white’, and Jaspers ‘I only see black; even when the sun is shining, it is still all black’. These perceptual distortions of colour occur in schizophrenia. In organic conditions,achromatopsia, which is the complete absence of colour, has been described after unilateral or bilateral occipital lesions, usually of the lingual and fusiform gyri.Dyschromatopsia refers to the perversion of colour perception and occurs after unilateral posterior lesions.

Visual Perception

Visual perception is the brain's ability to receive, interpret, and act upon visual stimuli. Perception is based on the following seven elements:

Visual discrimination

The ability to distinguish one shape from another.

Visual memory

The ability to remember a specific form when removed from your visual field.

Visual-spatial relationships

The ability to recognize forms that are the same but may be in a different spatial orientation.

Visual form constancy

The ability to discern similar forms that may be different in size, color, or spatial orientation and to consistently match the similar forms.

Visual sequential memory

The ability to recall two to seven items in sequence with vision occluded.

Visual figure/ground

The ability to discern discrete forms when camouflaged or partially hidden.

Visual closure

The ability to recognize familiar forms that are only partially completed.

Visual perception

Visual perception is the end product of the processing or reinterpretation by the cortex of sensory responses made by the retina to visual stimuli. However, a strict separation of cortical and retinal events does not occur as some degree of processing takes place in the retina and, conversely, certain processes such as instantaneous parallax (see later) occur so quickly that it is difficult to believe they occur exclusively at a cortical level. In addition, perception should not be considered solely as the end product of the processing of sensory information. Instead, it is part of the ‘action–perception cycle’, in which perception modifies activity, which then modifies perception in a continuous cyclic pattern, the boundaries of which become indistinct (Wexler and Boxtel, 2005). Motor activity (head and eye positioning, etc.), therefore, is central to perceptual processes such as stereopsis (see later) and detection of colour (see earlier).

As previously mentioned, there are many different types of visual stimuli, each of which may produce one or more different psychophysical perceptual responses. Sensory perception occurring at an elemental level encompasses visual stimuli such as luminosity, flicker, colour and form, because it involves simple processing of features such as points and lines or wavelengths. However, even such an apparently fundamental function as visual acuity determination involves higher levels of processing because it is more than simply a point-to-point projection of the retina on the cortex.

Evidence for higher integrative activity at the cortical level comes from illusions such as the Schrödinger staircase and Rubin’s vase as well as more specific illusions that involve both space and time such as the tilt illusions (Box 5.11). A clear example of the role of cortical function in visual perception is the phenomenon of colour constancy in which large variations in the chromaticity of an object, induced for instance by changing the wavelength of theilluminating light of the object, do not alter the perceived colour of the object: a yellow banana remains yellow even when illuminated by a green light (see earlier).

Our understanding of these processes has been greatly advanced by the careful analysis of both the stimuli and the responses and has allowed specific functions to be attributed to discrete regions of the cortex.

5.1 Property 1: Vision is a primary source of information

Visual perception is a primary source of information as people interpret and make sense of the world around them. Indeed, when multiple sources of input rival, visual information often receives priority (Kassuba, T., Klinge, C., Hölig, C., Röder, B., & Siebner, H.R. (2013); McGurk & MacDonald, 1976; Spence, Parise, & Chen, 2012). For example, baseball batters who received discrepant visual, auditory, and tactile information about the success of their swing prioritized the visual information they receive (Gray, 2009). The primacy of vision arguably occurs for several reasons. First, human eyes are biologically favored as input mechanisms. Seventy percent of the body's entire set of sensory receptors are located on the retinas (Spaulding, 2008), and two-thirds of the neural firings in the brain per second come directly from the visual cortex (Sells & Fixot, 1957). Moreover, approximately 30% of the entire cerebral cortex is devoted to visual processing (Sheth & Young, 2016). Second, human sight is tremendously powerful. For example, people can see extremely far distances, as far as the Triangulum Galaxy 3.14 million light years away on a clear night (Juan, 2006). Priority status is ascribed to vision, a powerful and efficient data information collection system. As a result, vision is especially well-situated to monitor goal progress, assess discrepancies, and detect signs of problems in the environment to assist in goal pursuit.

Impaired vision and visual perception.

Vision is critical in recovery of many motor functions because it is responsible for much of the feedforward, or anticipatory, control of movement and the initial development of a movement pattern. For example, balance can be maintained through the visual system by modifying synergies before surface change occurs. Feedback through the peripheral field via the movement of the visual array on the retina can also trigger balance responses. Campbell83 found problems with visual functions in most patients with mild to moderate TBI; these problems involved poor visual acuity (48%) and problems with vergence (85%), which can cause blurring and doubling of vision, and smooth pursuit (63%), which can cause a “jumping” of the visual image.

Some patients are able to use their hands for grasp and release, in spite of severe somatosensory deficits, when they are able to use vision to guide the motion. Many of the standard movement tests should be performed with and without vision.

General visual functions can be screened by the physical or occupational therapist as follows:

Tracking is assessed by use of an H pattern of movement of the object being tracked with the eyes and not with head movement. The examiner observes any nystagmus or refixation saccades. Eye muscle paralysis can be observed during tracking if the patient cannot move the eye(s) laterally, up, down, or medially.

Focus, or accommodation, can be checked by observing constriction and dilation of the pupil. Constriction occurs as an object is moved toward the nose, and dilation as the object is moved away from the nose.

Binocular vision is controlled through feedback from blurred or doubled vision. This reflex signals whether the eyes and fovea are focused on a single point or target, as the images in both eyes fall on the same retinal points. A “cover test” can screen for binocular vision. The patient stares at an object at about 18 inches from the nose. The therapist covers one eye. If there is movement to adjust the remaining uncovered eye back to the object, both retinas may not be focusing on the same point. Observing whether light reflections fall on exactly the same place on both pupils is useful in evaluating binocular eye focus. Vergence testing can also be an indicator of binocular visual functions.

Visual fields can be grossly tested by having the patient look forward at a point (observer sits in front of the patient to be sure the patient remains focused straight ahead). The patient indicates when he or she first sees an object coming into the peripheral field from behind, or the “spotter” notes when the patient looks toward the object.

Vergence is tested by having the patient observe an object or pen tip as it is brought from about 20 inches away. The patient is told to follow the object with his or her eyes. The object is moved at a moderate speed toward the bridge of the nose, and the patient reports when the object becomes blurred or doubles. When typical convergence is present, there will be no blurring or doubling until the object is 2 inches away or closer, and when the object is moved back out, the patient will report the object as single within 4 inches.

Visual interactions with the vestibular system are assessed through the vestibuloocular reflex (VOR). This reflex allows people to maintain a fixed gaze on a target as the head moves. The object should not appear to blur, move, or double during head motion at various speeds.

Perceptual tests that evaluate how visual information is used include visual memory tests, cancellation tests, and figure-ground tests.

Visual acuity is tested using a Snellen eye chart. Poor acuity can affect balance responses. Neuro-optometrists and neuro-ophthalmologists are appropriate referrals for patients needing in-depth visual workups, especially when visual perception is involved. SeeChapter 28 for additional information on vision and visual testing.

The ecological approach

Gibson (1979) produced a highly influential treatise in visual perception, challenging the cognitive accounts of perception. At the heart of his theory was the notion that the environment contains perceptual invariants, such as texture gradients, and ‘affordances’ for behaviors such as grasping, that individuals can use to guide their behavior. Yet, PCT would state that it is the perception for these invariants within the organism that is controlled through behavior by reducing error between the reference value and current perception of the environment. An affordance only exists to the extent that it fulfills a goal, as is evident when one considers that most ‘objects’ such as handles, tools, and instruments are actually designed by human beings with preconceived functions in mind that are not merely present as ‘givens’ in the environment. Gibson's work does not provide the architecture to model his ideas, yet the field of ‘embodied cognition’ often draws upon Gibson's work to develop such models (e.g. Wilson & Golonka, 2012). Such models begin with the assumption that behavior is ultimately what is controlled, and thus their architecture diverges from PCT. 9

Core Symptoms

AN and BN are syndromes consisting of disturbances of a range of behaviors, including feeding, mood, impulse control, body image perception, as well as other domains. The most striking features are related to eating and body image. In AN, an inexplicable fear of weight gain and unrelenting obsession with fatness, even in the face of increasing cachexia, accounts for a protracted course, extreme medical and psychological morbidity, and standardized mortality rates exceeding those of all other psychiatric disorders. People with AN have stereotypic patterns of food choices. They severely restrict food intake, particularly fats and carbohydrates, but rarely stop eating completely; rather, they restrict their caloric intake to a few hundred calories per day. They tend to be vegetarians, have monotonous choices in food intake, select unusual combinations of foods and flavors, and have ritualized eating behaviors. BN usually emerges after a period of food restriction, which may or may not have been associated with weight loss. Binge eating is followed by either self-induced vomiting or some other means of compensation for the excess of food ingested. The majority of people with BN have irregular feeding patterns, and satiety may be impaired.

It has long been debated whether symptoms in individuals with AN and BN are cause or consequence of malnutrition. Confounding this understanding is the reality that most studies of symptoms have been done when individuals are ill. Particularly common in individuals with AN are personality traits of marked perfectionism, conformity, obsessionality, constriction of affect and emotional expressiveness, and reduced social spontaneity. Studies have shown that the majority of individuals with AN and BN exhibit childhood perfectionism, obsessive–compulsive personality patterns, and anxiety (particularly obsessive–compulsive disorder and social phobia), and these symptoms predate the onset of AN and BN. Because these characteristics typically are present in childhood, prior to the onset of the eating disorder, and persist even after long-term weight recovery, they may be traits and not merely epiphenomena of acute malnutrition and disordered eating behavior. Individuals with BN are also more likely to exhibit histories of behavioral dyscontrol, substance abuse, and overt family conflict in comparison to those with the restricting subtype of AN.

It is important to note that other ‘core’ symptoms are common in AN and BN. One of the most puzzling symptoms of AN is the severe and intense body image distortion in which emaciated individuals perceive themselves as fat. Individuals ill with AN in particular have stereotyped hyperactive motor behavior, anhedonic and restrictive personalities, reduced novelty seeking, and a lower incidence of alcohol and drug use. Neuropsychological findings, using a broad range of assessments, have been somewhat inconsistent. A more focused, hypothesis-driven approach, pioneered by Tchanturia, Treasure, and others, has been based on the observation that people with AN show, as core features, high harm avoidance, inflexibility of thinking, rigid behaviors around eating, and high perfectionism. In addition, there is inflexibility on cognitive tasks and an inability to change past patterns of thinking, which can be conceptualized as difficulties in set shifting. These symptoms are evident in individuals with AN both during the acute phase of the illness and after weight restoration. In addition, such difficulties in set shifting are shared by the healthy sisters of those with AN, raising the intriguing possibility that set shifting represents a potential endophenotype for genetic studies of AN. Individuals with AN show a rigid pattern of responding and an inability to change a pattern of response once a behavior has been initiated. They also seem to have difficulty accessing and using conventional strategies for problem solving, such as learning from making mistakes. Rather, they obsessively repeat the same strategies despite the fact that such strategies are maladaptive and are not productive. Moreover, they often fail to accurately recognize and incorporate affective and social stimuli in the environment. Most strikingly, denial of emaciation or being ill, lack of insight, and resistance to treatment are often present. These characteristic styles raise the question of whether there is some physiologic disturbance of executive brain mechanisms that detect errors or plan and verify actions.

Artificial intelligence

The English Oxford Living Dictionary defines AI as “The theory and development of computer systems able to perform tasks normally requiring human intelligence, such as visual perception, speech recognition, decision-making, and translation between languages.” AI has become integrated into teens’ daily lives in multiple ways, among them:

Siri, Alexa, Cortana, and “Hey Google” assistants can perform a number of tasks such as tasks such as check the weather, suggest the fastest driving route to work, play music, or order items online.

Facebook uses AI to recognize faces in pictures posted to personalize newsfeeds and to select ads based on searches or words/phrases used in messaging.

Pinterest uses AI to see or categorize objects posted and then recommends other similar products/items.

Instagram uses AI to recognize emojis. Gen Z users rely on emojis rather than slang text (e.g., LOL). Instagram AI can interpret the emoji used and recommend other or new emoji’s.

Chatbots are being used by online retail companies to “talk/text” with customers about questions they may have about a product or a service.

Crutzen, Peters, Portugal, Fisser, & Grolleman (2011) studied 929 teens of an average age of 15 and with variable levels of education as they interacted with the artificially intelligent chat agent Bzz (a chatbot) that answered questions about sex, drugs, and alcohol. The chatbot was viewed positively by teens, even those who did not have experience in this realm, and the frequency of use and duration of conversations were high, when compared to search engines and other sources of information. Chatbots are becoming more popular and can serve as a source of education, health promotion and risk reduction for teens.

As VR and AI become more widely available and utilized, further research on the effects, benefits, and risks of these technologies is ongoing and encouraged.

The role of sensory and memory cortices in thoughts

When we remember something or someone, e.g., the face of a loved person, there is the subjective impression of “seeing with the mind's eye.” The phenomenological similarity between visual imagery and visual perception has been noted long ago and suggests that at least some of the same neural bases are underlying both processes.

Studies in mental imagery have shown that visual imagery and visual perception share specialized brain areas (Kosslyn et al., 2001). Results have even shown that visual imagery activates most of the same areas that visual perception does, although some sensory processes may be engaged differently (Ganis, Thompson, & Kosslyn, 2004). Even when the content is specific, as in the case of a face compared with an object, the content-related activation in the ventral extrastriate visual cortex follows the same patterns when people are imagining faces or objects compared with when they are being perceived (Ishai, Ungerleider, & Haxby, 2000).

In the case of auditory imagery, neuroimaging studies have shown that, during inner speech and auditory imagery, the same brain regions related to auditory perception are activated, but visual areas show no activation (McGuire et al., 1996; Shergill et al., 2001).

The abovementioned evidence shows that thoughts use different cortical processing resources depending on their modality. Therefore, sensory cortices are actively involved in thoughts, but the question about how they are integrated to give rise to what we experience as a coherent mental representation in the form of imagery or mind wandering is something that only recently is starting to be elucidated.

In the same way that sensory cortices are involved in self-generated activity, memory systems also play an important role in the generation, maintenance, and manipulation of mental representations during mental imagery and mind wandering.

In the case of mental imagery, an important finding has shown that imagining events in the future share neural substrates with remembering past events (Addis et al., 2007). This finding that a common brain network underlies both memory and imagination may well depend on temporal orientation or other nontemporal factors, such as the subprocesses of scene construction, taking the perspective of other person or spatial navigation (Schacter et al., 2012). In any case, memory integration is key in highly integrated states such as mental imagery (Schlichting & Preston, 2015). Likewise, the generation of mental representations during self-generated thoughts relies on both episodic and semantic memories (Wang, Yue, & Huang, 2016), whereas working memory is important for the maintenance of these processes (Levinson, Smallwood, & Davidson, 2012).

Therefore, beyond future thinking, the hippocampus has an important role in scene construction that is a pillar in mental imagery, in general (Palombo, Hayes, Peterson, Keane, & Verfaellie, 2018). Besides, memory transformation is also important, and studies have found that this process involves the posterior hippocampus (connected to perceptual and spatial representational systems in the posterior neocortex) and the anterior hippocampus (connected to conceptual systems such as medial prefrontal cortex) (Sekeres, Winocur, & Moscovitch, 2018).

In the case of spontaneous mind wandering, the hippocampus has been showed to be a key structure in the neural architecture of mind wandering, shaping the phenomenology of self-generated thoughts. A study examined the frequency and phenomenology of mind wandering in patients with selective bilateral hippocampal damage. They found hippocampal damage changed the form and content of mind wandering from flexible, episodic, and scene based to abstract, non–scene based, and verbal (McCormick, Rosenthal, Miller, & Maguire, 2018).

In the following, we will discuss the role of the DMN in the integration of sensory information, semantic and episodic memory, and processes of scene construction to generate self-generated thoughts.

Feelings of Illumination and Penetration

Our insights often appear in the conscious mind as givens and have the same sense of immediacy as our sensory perception. We take what we perceive to be valid knowledge about the world, at least for the moment. Like visual perception, the perception is composed of interlocking strands that come together below awareness to form a meaningful whole. For this reason, the experience of insight has been referred to as “seeing that.” This inner seeing is, of course, one of the many meanings of the phrase a “blink of the eye.”

The metacognitive feeling of knowing that accompany moments of “seeing that” tends to be overshadowed by the insight itself, which quickly occupies the center of awareness. Nonetheless we can sometimes sense it as a quicksilver flash of illumination on the fringe of awareness, the proverbial light bulb above the comic strip character’s head, just as all relevant information coalesces below awareness. This feeling is probably easiest to capture when something else demands attention (such as a ringing phone or a crying baby) and the insight is lost. All that remains is a memory of the feeling of illumination.

The feeling of illumination can have a range of intensity. When it is particularly intense, it may appear in awareness as a sense of penetration or depth that shares billing in consciousness with the insight itself. The insight that initiated the vignette, for instance, was accompanied by a sense of being deeper than my three older bits of knowledge, and the final insight that synthesized all four ideas, much deeper still. The feeling of penetration or depth that sometimes accompanies an insight provides one measure of its cognitive coherence and how well it fits with all the other information in the system—thus its explaining power. The more penetrating the insight, the more encompassing it is, and the more efficiently it can organize all thought, not only at the conscious level but at an unconscious level as well. Thus the less likely it will be overturned.

Yet no instant of “seeing that” is necessarily permanent. A feeling of metacognitive discomfort might begin to overshadow the sense of comprehension and closure associated with the insight. The goals of the intuitive self are constantly readjusting. What seems like a worthy insight in one moment may need amending in the next. The momentary field of coherence that comes into focus in an instant of knowing might include only a limited amount of our potentially relevant conscious and unconscious information. Also, the limitations of an insight may emerge over time as some of its subtler implications rise to awareness.