Misplaced Pages

#334665

70-448: The FFA is located in the ventral stream on the ventral surface of the temporal lobe on the lateral side of the fusiform gyrus . It is lateral to the parahippocampal place area . It displays some lateralization , usually being larger in the right hemisphere . The FFA was discovered and continues to be investigated in humans using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies. Usually,

140-402: A bias for the caregivers they experience. Infants do not appear to use this area for the perception of faces. Recent fMRI work has found no face selective area in the brain of infants 4 to 6 months old. However, given that the adult human brain has been studied far more extensively than the infant brain, and that infants are still undergoing major neurodevelopmental processes, it may simply be that

210-402: A face recognition task, higher availability of D1 receptor was shown to be associated with higher BOLD level. This study showed that this association with D1 BP is only significant for FFG, not other brain regions. The researchers also showed the possibility that higher availability of dopamine D1 receptor may underlie better performance in face recognition task. Dopamine is known to be related to

280-570: A familiar face as opposed to an unfamiliar one. Participants were shown different pictures of faces that either had the same identity, familiar, or faces with separate identities, or unfamiliar. It found that participants were more accurate at matching familiar faces than unfamiliar ones. Using an fMRI, they also found that the participants that were more accurate in identifying familiar faces had more activity in their right fusiform face area and participants that were poor at matching had less activity in their right fusiform area. In 2020, scientists showed

350-443: A full representation of visual space. That is, it contains neurons whose receptive fields together represent the entire visual field. Visual information enters the ventral stream through the primary visual cortex and travels through the rest of the areas in sequence. Moving along the stream from V1 to AIT, receptive fields increase their size, latency, and the complexity of their tuning. For example, recent studies have shown that

420-411: A macroanatomical landmark for the fusiform face area (FFA), a functional subregion of the fusiform gyrus assumed to play a key role in processing faces . The fusiform gyrus has a contentious history that has recently been clarified. The term was first used in 1854 by Emil Huschke from Jena, Germany , who called the fusiform gyrus a "Spindelwulst" (lit. spindle bulge). He chose this term because of

490-433: A number of spatial disorders including: The ventral stream is associated with object recognition and form representation. Also described as the "what" stream, it has strong connections to the medial temporal lobe (which is associated with long-term memories ), the limbic system (which controls emotions), and the dorsal stream (which deals with object locations and motion). The ventral stream gets its main input from

560-407: A participant views images of faces, objects, places, bodies, scrambled faces, scrambled objects, scrambled places, and scrambled bodies. This is called a functional localizer . Comparing the neural response between faces and scrambled faces will reveal areas that are face-responsive, while comparing cortical activation between faces and objects will reveal areas that are face-selective. The human FFA

630-483: A similarly impaired pace as face recognition. Studies of late patients of autism have discovered that autistic people have lower neuron densities in the FFA. This raises an interesting question, however: Is the poor face perception due to a reduced number of cells or is there a reduced number of cells because autistic people seldom perceive faces? Asked simply: Are faces simply objects with which every person has expertise? There

700-480: A subject's ability to reproduce speech (typically by repetition), though it has no influence on the subject's ability to comprehend spoken language. This shows that conduction aphasia must reflect not an impairment of the auditory ventral pathway but instead of the auditory dorsal pathway. Buchsbaum et al found that conduction aphasia can be the result of damage, particularly lesions, to the Spt (Sylvian parietal temporal). This

770-500: Is a model of the neural processing of vision as well as hearing . The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual systems. Recently there seems to be evidence of two distinct auditory systems as well. As visual information exits the occipital lobe , and as sound leaves the phonological network, it follows two main pathways, or "streams". The ventral stream (also known as

SECTION 10

#1732877050335

840-430: Is achieved in a way that dopamine first influence post-synaptic potential, and then further cause BOLD activity increase in the local area. This link between post-synaptic BOLD activity increase and dopamine release can be explained by blockage of dopamine reuptake. The fusiform gyrus has been speculated to be associated with various neurological phenomena. Some researchers think that the fusiform gyrus may be related to

910-408: Is also good at detecting and analyzing movements. The dorsal stream commences with purely visual functions in the occipital lobe before gradually transferring to spatial awareness at its termination in the parietal lobe. The posterior parietal cortex is essential for "the perception and interpretation of spatial relationships, accurate body image, and the learning of tasks involving coordination of

980-476: Is causal support for the role of these functional clusters in perceiving the facial image. While it is generally agreed that the FFA responds more to faces than to most other categories, there is debate about whether the FFA is uniquely dedicated to face processing, as proposed by Nancy Kanwisher and others, or whether it participates in the processing of other objects. The expertise hypothesis, as championed by Isabel Gauthier and others, offers an explanation for how

1050-434: Is evidence supporting the FFA's evolutionary face-perception. Case studies into other dedicated areas of the brain may suggest that the FFA is intrinsically designed to recognize faces. Other studies have recognized areas of the brain essential to recognizing environments and bodies. Without these dedicated areas, people are incapable of recognizing places and bodies. Similar research regarding prosopagnosia has determined that

1120-549: Is part of the temporal lobe and occipital lobe in Brodmann area 37 . The fusiform gyrus is located between the lingual gyrus and parahippocampal gyrus above, and the inferior temporal gyrus below. Though the functionality of the fusiform gyrus is not fully understood, it has been linked with various neural pathways related to recognition. Additionally, it has been linked to various neurological phenomena such as synesthesia , dyslexia , and prosopagnosia . Anatomically,

1190-609: Is shown by the Spt's involvement in acquiring new vocabulary, for while experiments have shown that most conduction aphasiacs can repeat high-frequency, simple words, their ability to repeat low-frequency, complex words is impaired. The Spt is responsible for connecting the motor and auditory systems by making auditory code accessible to the motor cortex. It appears that the motor cortex recreates high-frequency, simple words (like cup ) in order to more quickly and efficiently access them, while low-frequency, complex words (like Sylvian parietal temporal ) require more active, online regulation by

1260-592: Is similar to a face-specific ERP component N170 . The authors suggest that face perception evoked by face-like objects is a relatively early process, and not a late cognitive reinterpretation phenomenon. One case study of agnosia provided evidence that faces are processed in a special way. A patient known as C. K., who suffered brain damage as a result of a car accident, later developed object agnosia. He experienced great difficulty with basic-level object recognition, also extending to body parts, but performed very well at recognizing faces. A later study showed that C. K.

1330-448: Is situated at the basal surface of the temporal and occipital lobes and is delineated by the collateral sulcus (CoS) and occipitotemporal sulcus (OTS), respectively. The OTS separates the fusiform gyrus from the inferior temporal gyrus (located laterally in respect to the fusiform gyrus) and the CoS separates the fusiform gyrus from the parahippocampal gyrus (located medially in respect to

1400-482: The arcuate fasciculus , which is vital for both speech and language comprehension, as the arcuate fasiculus makes up the connection between Broca and Wernicke's areas. Goodale & Milner's innovation was to shift the perspective from an emphasis on input distinctions, such as object location versus properties, to an emphasis on the functional relevance of vision to behaviour, for perception or for action. Contemporary perspectives however, informed by empirical work over

1470-408: The parvocellular (as opposed to magnocellular ) layer of the lateral geniculate nucleus of the thalamus . These neurons project to V1 sublayers 4Cβ, 4A, 3B and 2/3a successively. From there, the ventral pathway goes through V2 and V4 to areas of the inferior temporal lobe : PIT (posterior inferotemporal), CIT (central inferotemporal), and AIT (anterior inferotemporal). Each visual area contains

SECTION 20

#1732877050335

1540-460: The "intra-gyral sulcus of the fusiform lobule". The exact functionality of the fusiform gyrus is still disputed, but there is relative consensus on its involvement in the following pathways: In 2003, V. S. Ramachandran collaborated with scientists from the Salk Institute for Biological Studies in order to identify the potential role of the fusiform gyrus within the color processing pathway in

1610-526: The "what pathway") leads to the temporal lobe, which is involved with object and visual identification and recognition . The dorsal stream (or, "where pathway") leads to the parietal lobe, which is involved with processing the object's spatial location relative to the viewer and with speech repetition. Several researchers had proposed similar ideas previously. The authors themselves credit the inspiration of work on blindsight by Weiskrantz , and previous neuroscientific vision research. Schneider first proposed

1680-532: The FFA becomes selective for faces in most people. The expertise hypothesis suggests that the FFA is a critical part of a network that is important for individuating objects that are visually similar because they share a common configuration of parts. Gauthier et al., in an adversarial collaboration with Kanwisher, tested both car and bird experts, and found some activation in the FFA when car experts were identifying cars and when bird experts were identifying birds. This finding has been replicated, and expertise effects in

1750-431: The FFA has other functions regarding emotion. The FFA is differentially activated by faces exhibiting different emotions. A study has determined that the FFA is activated more strongly by fearful faces than neutral faces. This implies that the FFA has functions in processing emotion despite its downstream processing and questions its evolutionary purpose to identify faces. Ventral stream The two-streams hypothesis

1820-516: The FFA have been found for other categories such as chess displays and X-rays. Recently, it was found that the thickness of the cortex in the FFA predicts the ability to recognize faces as well as vehicles. A 2009 magnetoencephalography study found that objects incidentally perceived as faces, an example of pareidolia , evoke an early (165-millisecond) activation in the FFA, at a time and location similar to that evoked by faces, whereas other common objects do not evoke such activation . This activation

1890-403: The FFA is essential to the recognition of unique faces. However, these patients are capable of recognizing the same people normally by other means, such as voice. Studies involving language characters have also been conducted in order to ascertain the role of the FFA in face recognition. These studies have found that objects, such as Chinese characters, elicit a high response in different areas of

1960-409: The FFA is not located in an anatomically familiar area. It may also be that activation for many different percepts and cognitive tasks in infants is diffuse in terms of neural circuitry, as infants are still undergoing periods of neurogenesis and neural pruning ; this may make it more difficult to distinguish the signal, or what we would imagine as visual and complex familiar objects (like faces), from

2030-409: The FFA is tuned for behaviorally relevant facial features. An electrocorticography study found that the FFA is involved in multiple stages of face processing, continuously from when people see a face until they respond to it, demonstrating the dynamic and important role the FFA plays as part of the face perception network. Another study found that there is stronger activity in the FFA when a person sees

2100-404: The FFA than those areas that elicit a high response from faces. This data implies that certain areas of the FFA have evolutionary face-perception purposes. The FFA is underdeveloped in children and does not fully develop until adolescence. This calls into question the evolutionary purpose of the FFA, as children show the ability to differentiate faces. Three-day-old babies have been shown to prefer

2170-432: The Spt, language acquisition is impaired. The information then moves onto the articulatory network, which is divided into two separate parts. The articulatory network 1, which processes motor syllable programs, is located in the left posterior inferior temporal gyrus and Brodmann's area 44 (pIFG-BA44). The articulatory network 2 is for motor phoneme programs and is located in the left M1-vBA6. Conduction aphasia affects

Fusiform face area - Misplaced Pages Continue

2240-430: The Spt. This explains why conduction aphasiacs have particular difficulty with low-frequency words which requires a more hands-on process for speech production. "Functionally, conduction aphasia has been characterized as a deficit in the ability to encode phonological information for production," namely because of a disruption in the motor-auditory interface. Conduction aphasia has been more specifically related to damage of

2310-522: The Sylvian fissure at the parietal-temporal boundary). The spt is important for perceiving and reproducing sounds. This is evident because its ability to acquire new vocabulary, be disrupted by lesions and auditory feedback on speech production, articulatory decline in late-onset deafness and the non-phonological residue of Wernicke's aphasia; deficient self-monitoring. It is also important for the basic neuronal mechanisms for phonological short-term memory. Without

2380-656: The V4 area is responsible for color perception in humans, and the V8 (VO1) area is responsible for shape perception, while the VO2 area, which is located between these regions and the parahippocampal cortex, integrates information about the color and shape of stimuli into a holistic image. All the areas in the ventral stream are influenced by extraretinal factors in addition to the nature of the stimulus in their receptive field. These factors include attention , working memory , and stimulus salience . Thus

2450-500: The ambiguity in FFA activation, as the FFA is activated by both familiar objects and faces. A study regarding novel objects called greebles determined this phenomenon. When first exposed to greebles, a person's FFA was activated more strongly by faces than by greebles. After familiarising themselves with individual greebles or becoming a greeble expert, a person's FFA was activated equally by faces and greebles. Likewise, children with autism have been shown to develop object recognition at

2520-581: The angular and fusiform gyri has been observed in the average brain, implying that the fusiform gyrus regularly communicates with the visual pathway. Portions of the fusiform gyrus are critical for face and body recognition. It is believed that portions of the left hemisphere fusiform gyrus are used in word recognition . Further research by MIT scientists showed that the left and right fusiform gyri played different roles, which subsequently interlinked. The left fusiform gyrus recognizes "face-like" features in objects that may or may not be actual faces, whereas

2590-457: The area is also activated in people born blind. The fusiform face area (FFA) is a part of the brain located in the fusiform gyrus with a debated purpose. Some researchers believe that the FFA is evolutionary purposed for face perception . Others believe that the FFA discriminates between any familiar stimuli. Psychologists debate whether the FFA is activated by faces for an evolutionary or expertise reason. The conflicting hypotheses stem from

2660-464: The auditory dorsal pathway is necessary because, "learning to speak is essentially a motor learning task. The primary input to this is sensory, speech in particular. So, there must be a neural mechanism that both codes and maintains instances of speech sounds, and can use these sensory traces to guide the tuning of speech gestures so that the sounds are accurately reproduced." In contrast to the ventral stream's auditory processing, information enters from

2730-403: The body in space". It contains individually functioning lobules. The lateral intraparietal sulcus (LIP) contains neurons that produce enhanced activation when attention is moved onto the stimulus or the animal saccades towards a visual stimulus, and the ventral intraparietal sulcus (VIP) where visual and somatosensory information are integrated. Damage to the posterior parietal cortex causes

2800-463: The brain. Examining the relationship within the pathway specifically in cases of synesthesia, Ramachandran found that synesthetes on average have a higher density of fibers surrounding the angular gyrus . The angular gyrus is involved in higher processing of colors. The fibers relay shape information from the fusiform gyrus to the angular gyrus in order to produce the association of colors and shapes in grapheme-color synesthesia. Cross-activation between

2870-428: The broad relative specializations of dorsal and ventral streams. However, to progress the field, we may need to abandon the idea that these streams work largely independently of one other, and to address the dynamic details of how the many visual brain areas arrange themselves from task to task into novel functional networks. Fusiform gyrus The fusiform gyrus , also known as the lateral occipitotemporal gyrus ,

Fusiform face area - Misplaced Pages Continue

2940-431: The disorder known as prosopagnosia , or face blindness. Research has also shown that the fusiform face area, the area within the fusiform gyrus, is heavily involved in face perception but only to any generic within-category identification that is shown to be one of the functions of the fusiform gyrus. Abnormalities of the fusiform gyrus have also been linked to Williams syndrome . Fusiform gyrus has also been involved in

3010-442: The dissociation was not as strong as first thought. A 2009 review of the accumulated evidence for the model concluded that whilst the spirit of the model has been vindicated the independence of the two streams has been overemphasised. Goodale & Milner themselves have proposed the analogy of tele-assistance, one of the most efficient schemes devised for the remote control of robots working in hostile environments. In this account,

3080-441: The dorsal 'action' stream transforms incoming visual information to the requisite egocentric (head-centered) coordinate system for skilled motor planning . The model also posits that visual perception encodes spatial properties of objects, such as size and location, relative to other objects in the visual field; in other words, it utilizes relative metrics and scene-based frames of reference. Visual action planning and coordination, on

3150-408: The dorsal stream is viewed as a semi-autonomous function that operates under guidance of executive functions which themselves are informed by ventral stream processing. Thus the emerging perspective within neuropsychology and neurophysiology is that, whilst a two-systems framework was a necessary advance to stimulate study of the highly complex and differentiated functions of the two neural pathways;

3220-416: The execution of the grasping act. Norman proposed a similar dual-process model of vision, and described eight main differences between the two systems consistent with other two-system models. The dorsal stream is proposed to be involved in the guidance of actions and recognizing where objects are in space. The dorsal stream projects from the primary visual cortex to the posterior parietal cortex . It

3290-532: The existence of two visual systems for localisation and identification in 1969. Ingle described two independent visual systems in frogs in 1973. Ettlinger reviewed the existing neuropsychological evidence of a distinction in 1990. Moreover, Trevarthen had offered an account of two separate mechanisms of vision in monkeys back in 1968. In 1982, Ungerleider and Mishkin distinguished the dorsal and ventral streams, as processing spatial and visual features respectively, from their lesion studies of monkeys – proposing

3360-416: The face of their mother. Babies as early as three months old have shown the ability to distinguish between faces. During this time, babies may exhibit the ability to differentiate between genders, with some evidence suggesting that they prefer faces of the same sex as their primary caregiver. It is theorized that, in terms of evolution, babies focus on women for food, although the preference could simply reflect

3430-411: The focus of some criticism of the model due to the perceived over-reliance on findings from a single case. Goodale and Milner amassed an array of anatomical, neuropsychological, electrophysiological, and behavioural evidence for their model. According to their data, the ventral 'perceptual' stream computes a detailed map of the world from visual input, which can then be used for cognitive operations, and

3500-447: The fusiform gyrus is the largest macro-anatomical structure within the ventral temporal cortex , which mainly includes structures involved in high-level vision . The term fusiform gyrus (lit. "spindle-shaped convolution") refers to the fact that the shape of the gyrus is wider at its centre than at its ends. This term is based on the description of the gyrus by Emil Huschke in 1854. (see also section on history ). The fusiform gyrus

3570-517: The fusiform gyrus). The fusiform gyrus can be further delineated into a lateral and medial portion, as it is separated in its middle by the relatively shallow mid-fusiform sulcus (MFS). Thus, the lateral fusiform gyrus is delineated by the OTS laterally and the MFS medially. Likewise, the medial fusiform gyrus is delineated by the MFS laterally and the CoS medially. Importantly, the mid-fusiform sulcus serves as

SECTION 50

#1732877050335

3640-607: The idea that skilled actions such as grasping are not affected by pictorial illusions. Moreover, recent neuropsychological research has questioned the validity of the dissociation of the two streams that has provided the cornerstone of evidence for the model. The dissociation between visual agnosia and optic ataxia has been challenged by several researchers as not as strong as originally portrayed; Hesse and colleagues demonstrated dorsal stream impairments in patient DF; Himmelbach and colleagues reassessed DF's abilities and applied more rigorous statistical analysis demonstrating that

3710-417: The mid-fusiform sulcus was coined by Gustav Retzius in 1896. He was the first to describe the sulcus sagittalis gyri fusiformis (today: mid-fusiform sulcus), and correctly determined that a sulcus divides the fusiform gyrus into lateral and medial partitions. W. Julius Mickle mentioned the mid-fusiform sulcus in 1897 and attempted to clarify the relation between temporal sulci and the fusiform gyrus, calling it

3780-416: The nickname of the dorsal stream to be updated to the "how" pathway. The dorsal stream is interconnected with the parallel ventral stream (the "what" stream) which runs downward from V1 into the temporal lobe . The dorsal stream is involved in spatial awareness and guidance of actions (e.g., reaching). In this it has two distinct functional characteristics—it contains a detailed map of the visual field, and

3850-502: The noise, including static firing rates of neurons, and activity that is dedicated to a different task entirely than the activity of face processing. Infant vision involves only light and dark recognition, recognizing only major features of the face, activating the amygdala . These findings question the evolutionary purpose of the FFA. Studies into what else may trigger the FFA validates arguments about its evolutionary purpose. There are countless facial expressions humans use that disturb

3920-458: The original where vs what distinction. Though this framework was superseded by that of Milner & Goodale, it remains influential. One hugely influential source of information that has informed the model has been experimental work exploring the extant abilities of visual agnosic patient D.F. The first, and most influential report, came from Goodale and colleagues in 1991 and work is still being published on her two decades later. This has been

3990-404: The other hand, uses absolute metrics determined via egocentric frames of reference, computing the actual properties of objects relative to the observer. Thus, grasping movements directed towards objects embedded in size-contrast-ambiguous scenes have been shown to escape the effects of these illusions, as different frames of references and metrics are involved in the perception of the illusion versus

4060-469: The past two decades, offer a more complex account than a simple separation of function into two-streams. Recent experimental work for instance has challenged these findings, and has suggested that the apparent dissociation between the effects of illusions on perception and action is due to differences in attention, task demands, and other confounds. There are other empirical findings, however, that cannot be so easily dismissed which provide strong support for

4130-421: The perception of emotions in facial stimuli. However, individuals with autism show little to no activation in the fusiform gyrus in response to seeing a human face. Recent research has seen activation of the fusiform gyrus during subjective grapheme–color perception in people with synaesthesia . The effect of the fusiform gyrus in grapheme sense seems somewhat more clear as the fusiform gyrus seems to play

4200-412: The primary auditory cortex into the posterior superior temporal gyrus and posterior superior temporal sulcus. From there the information moves to the beginning of the dorsal pathway, which is located at the boundary of the temporal and parietal lobes near the Sylvian fissure. The first step of the dorsal pathway begins in the sensorimotor interface, located in the left Sylvian parietal temporal (Spt) (within

4270-461: The primary auditory cortex. In this pathway, phonemes are processed posteriorly to syllables and environmental sounds. The information then joins the visual ventral stream at the middle temporal gyrus and temporal pole. Here the auditory objects are converted into audio-visual concepts. The function of the auditory dorsal pathway is to map the auditory sensory representations onto articulatory motor representations. Hickok & Poeppel claim that

SECTION 60

#1732877050335

4340-424: The reality is more likely to involve considerable interaction between vision-for-action and vision-for-perception. Robert McIntosh and Thomas Schenk summarize this position as follows: We should view the model not as a formal hypothesis, but as a set of heuristics to guide experiment and theory. The differing informational requirements of visual recognition and action guidance still offer a compelling explanation for

4410-468: The reward system. The dopaminergic system shows an active response to stimuli that predict possible rewards. As a social demand, a face recognition task could be a cognition process that involves dopamine, which can elicit a reinforcement feedback. A 2007 study investigated how dopamine may regulate FFG activity during a face recognition task. It indicated that BOLD activity can be modulated by dopamine's influence on postsynaptic D1 receptors. The regulation

4480-408: The right fusiform gyrus determines if that recognized face-like feature is, in fact, a face. In a 2015 study, dopamine was proposed to play a key role in face recognition task and was considered to be related to neural activity in fusiform gyrus. By studying the correlation between the binding potential (BP) of dopamine D1 receptor by PET and blood-oxygen-level-dependent (BOLD) in fMRI scan during

4550-500: The similarity that the respective cerebral gyrus bears to the shape of a spindle, or fusil, due to its wider central section. At first, researchers located the fusiform gyrus in other mammals as well, without taking into account the variations in gross organizations of other species' brains. Today, the fusiform gyrus is considered to be specific to hominoids . This is supported by research showing only three temporal gyri and no fusiform gyrus in macaques. The first accurate definition of

4620-444: The structure of the face. These disruptions and emotions are first processed in the amygdala and later transmitted to the FFA for facial recognition. This data is then used by the FFA to determine more static information about the face. The fact that the FFA is so far downstream in the processing of emotion suggests that it has little to do with emotion perception and instead deals in face perception. Recent evidence, however, shows that

4690-411: The ventral stream does not merely provide a description of the elements in the visual world—it also plays a crucial role in judging the significance of these elements. Damage to the ventral stream can cause inability to recognize faces or interpret facial expression. Along with the visual ventral pathway being important for visual processing, there is also a ventral auditory pathway emerging from

4760-442: Was first described by Justine Sergent in 1992 and later named by Nancy Kanwisher in 1997 who proposed that the existence of the FFA is evidence for domain specificity in the visual system. Studies have recently shown that the FFA is composed of functional clusters that are at a finer spatial scale than prior investigations have measured. Electrical stimulation of these functional clusters selectively distorts face perception, which

4830-423: Was initially termed the "where" pathway since it was thought that the dorsal stream processes information regarding the spatial properties of an object. However, later research conducted on a famous neuropsychological patient, Patient D.F., revealed that the dorsal stream is responsible for processing the visual information needed to construct the representations of objects one wishes to manipulate. Those findings led

4900-416: Was unable to recognize faces that were inverted or otherwise distorted, even in cases where they could easily be identified by normal subjects. This is taken as evidence that the fusiform face area is specialized for processing faces in a normal orientation. Studies using functional magnetic resonance imaging and electrocorticography have demonstrated that activity in the FFA codes for individual faces and

#334665