Interindividual differences in perception

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Interindividual differences in perception describes the effect that differences in brain structure or factors such as culture, upbringing and environment have on the perception of humans. Interindividual (differing from person to person) variability is usually regarded as a source of noise for research. However, in recent years, it has become an interesting source to study sensory mechanisms and understand human behavior. With the help of modern neuroimaging methods such as fMRI and EEG, individual differences in perception could be related to the underlying brain mechanisms. This has helped to explain differences in behavior and cognition across the population. The present study using MRS provides direct evidence showing that the excitatory process in the suprasensory areas is linked to the individual differences in visual motion perception. The neurotransmitter concentration in the higher areas that execute cognitive functions is related to the interindividual variability in the perception of visual motion. [1] Common methods include studying the perception of illusions, as they can effectively demonstrate how different aspects such as culture, genetics and the environment can influence human behavior.

Contents

Optical Illusions

Bistable Motion

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Two bistable motion quartets with differing aspect ratios

A motion quartet is a bistable stimulus - it consists of two dots that change their position from frame to frame. This position change can either be interpreted as horizontal or vertical movement by viewers, and this experience can switch during viewing between interpretations. Depending on the aspect ratio of the two dots' positions, one or the other state is perceived longer or more often. At an aspect ratio of one, the illusion is biased towards the vertical perception. The reason for this might be the way the human brain processes the signals from both eyes in the visual system. The right half of an eye's field of view is processed by the left hemisphere, and the left half by the right hemisphere. A stimulus moving vertically only involves one field of view and so one hemisphere, while a stimulus moving vertically from one field of view to the other involves both hemispheres, and requires communication between them. The delay caused by this additional signalling might be the cause for the bias. [2] There are also individual differences in the way the motion quartet is perceived: Some people require a different aspect ratio to perceive both axes of movement than others. A study using diffusion tensor imaging further showed differences in the structure of the corpus callosum, the primary connection between the two hemispheres, might be the origin of these differences. [3]

Object size estimation

There exist a variety of illusions that make objects appear bigger or smaller compared to their real size. Two such illusions are the Ebbinghaus and the Ponzo illusions. The Ebbinghaus illusion makes a dot seem bigger because it is surrounded by smaller dots, while the Ponzo illusion exploits human perspective processing by making a dot appear bigger because it seems farther away. Schwarzkopf et al. [4] found that the size of the primary visual cortex (V1) has an effect on the magnitude of these illusions. The larger the subject's V1 surface area was, the less the subjects fell for the illusion. This is hypothesized to be due to the fact that a larger V1 dedicated to the same portion of the visual field means a lesser effect of later, fixed-size visual areas (which are the ones that are responsible for the illusion effect). [4]

Auditory Illusions

McGurk Effect

The McGurk effect is an auditory illusion in which people perceive a different syllable when incongruent audiovisual speech is presented: an auditory syllable "ba" is presented while the mouth movement is "ga". As a result, the listener perceives the syllable "da". However, according to Gentilucci and Cattaneo (2005), not everyone perceives this illusion; only about 26% to 98% of the population are susceptible to this illusion. [5] One of the psychological models that explains the interindividual differences in speech perception is the fuzzy logic model of speech perception [6] According to this model, a categorization process is carried out when processing speech sounds. When listening to a stimulus, the features of the acoustic signal are analyzed. Subsequently, this signal is compared with the features that are stored in the memory; finally the sound is classified into the category that best fits. However, this classification may have a blurred boundary respectively to the category which the sound belongs to. As a result, the final decision may depend on integration of multiple sources of information. When the McGurk effect is presented the auditory and visual components of the speech are separately evaluated before being integrated. In those who perceive the McGurk effect, the visual information has a higher influence on the perception of the ambiguous audiovisual information and thus the sound is classified as "da".

Many studies have concluded that the area responsible for the perception of this phenomenon is the left superior temporal sulcus(STS). [7] This area is critical for the multisensory integration of visual and auditory information during speech perception. Moreover, there is a correlation between the activation of the STS and the perception of the McGurk effect. In that sense, if the left STS correctly integrates the mismatched audiovisual information, a McGurk effect is perceived; if the left STS is not active, the visual and auditory information are not integrated and thus a McGurk effect is not perceived.

In one study [7] blood-oxygen-level dependent functional magnetic resonance imaging (BOLD fMRI) was used to measure the brain activity in perceivers and non-perceivers of the McGurk effect while presented with congruent audiovisual syllables, McGurk audiovisual syllables (auditory "ba" + visual "ga" producing perception of "da"), and non-McGurk incongruent syllables( auditory "ga" + visual "ba" producing auditory perception of "ga"). The researchers found that there was a positive correlation between the amplitude of response in the left STS and the probability of perceiving the McGurk effect. In other words, the subject with the weakest STS activation to incongruent speech had the smallest probability of experiencing a McGurk percept; whereas the subject with the strongest STS response had the highest probability. [8]

Beauchamp et al. (2010) highlight the critical role of the left STS in audiovisual integration. [9] They applied single pulses of transcranial magnetic stimulation (TMS) to the STS of McGurk perceivers during presentation of McGurk stimuli. The perception of the McGurk effect decreased from 94% to 43% and the subjects reported perceiving only the auditory syllable. Following from that, Beauchamp et al. conclude that the left STS is crucial for the audiovisual integration and thus for the perception of the McGurk effect.

Moreover, another study [10] suggests that the basis of the interindividual differences in the perception of McGurk effect lies in the eye movements of the subject when viewing the talker's face. The experimenters carried out an eye tracking study and measured the eye movements of the participants while viewing audiovisual speech. They found that people who spent more time fixating the mouth of the talker were the more likely to perceive the McGurk effect than those who rarely fixated on the mouth of the speaker.

Other auditory illusions

Representation of the pitch class circle with respect to tone height Pitch class space.svg
Representation of the pitch class circle with respect to tone height

Interindividual differences have also been researched for the Tritone paradox illusion. In this illusion, the subject successively listens to two tones, which are separated by a half octave. Each tone is made of a set of harmonics which have an octave relation. The listener has to decide if the two tones have a descending or ascending relation. According to Diana Deutsch, [11] the perception of the tones is influenced by the language spoken by the listener. The listener has a circular representation of the pitch of sounds that are common in their culture and based on that develops a pitch range of their speaking voice, which determines the orientation of the pitch class with respect to the height; when a given tone is in this range, it is taken as the highest position along the circle and depending on the second tone, the person perceives the pattern as ascending or descending. Deutsch [11] found that for people from California, the tone in the highest position of the pitch-class circle is around C# and D whereas for people from southern England it is around G. According to those results, Deutsch hypothesized that the orientation of the pitch-class circle with respect to the height is similar for individuals from the same linguistic group and varies for individuals from different linguistic groups.

Other illusions found by Deutsch whose interpretation depends on interindividual differences is the phantom words illusion. [12] This illusion consists of the continuous presentation of two meaningless syllables. In order to experience the illusion, it is necessary that the listener sits between two loudspeakers, one to the left and the other to the right. The syllables are presented offset in time, in such a way that while one syllable is coming from the left, the other syllable is coming from the right loudspeaker. It was shown that after a period of time, people start hearing words. According to Deutsch, the perceived words depend on the language spoken by the listener, their knowledge and their expectations. According to Shinn-Cunningham (2008), [13] when the information is incomplete or contradictory, the perceptual system often fills this gaps with plausible interpretations and in that way allows new information to be efficiently processed.

Effect of Culture on Perception

The framed line test Frame and Line Test.svg
The framed line test

Several studies have shown that differences between individuals play a significant role in determining how a stimulus is perceived. These differences among people, in turn, are greatly influenced by one's own socio-cultural contexts. The research indicates that cultural factors influence the process of perception not just on lower-level (such as object perception and attention deployment), but also on the higher-order functions (such as theory of mind and emotion recognition). [14] [15] [16]

The two major cultures analyzed in these studies were mostly Western and East Asian cultures because of the considerable differences in the social structure and practices. Western culture was referred to as an analytical culture whereas Eastern culture was referred more as a holistic culture. [17] More specifically, individualism and freedom are the predominant values in Western societies, which in turn demand interpretation of an object in its absolute terms independent of its context. In contrast, Eastern culture is known for its emphasis on collectivism and interdependence on each other, where interpretation of an object is often in relation with its context [18]

A pioneer study examining these cultural differences in visual perception was conducted by Kitayama et al. (2003). [16] The findings of that study provide behavioural evidence on how cultural factors affect visual perception and attention deployment. For the study, Americans and Japanese were taken as subjects. The visual stimulus shown to the subjects consisted of a square figure with a line hanging from the centre (the framed line test). First was the absolute condition, where the task was to redraw the line on the centre of the square in its absolute length, to a new square box independent of its size. Second was the relative condition, in which the task was to redraw the line proportionally similar to context of the new square box. The results show that Americans perform better in the absolute task which requires analytical processing of stimulus independent of it context, whereas the Japanese performed better at the relative task which demands the holistic processing of the stimulus in relation to its context.

In line with these findings, Hedden and colleagues (2009) [19] used the same visual stimuli to investigate the neural activity with the help of fMRI. Participants of the study were asked to judge the length of a vertical line, either including the contextual information or ignoring it. The results revealed that separate brain regions were employed while performing the task, either incorporating the contextual information or avoiding it, based on one's own culture. The areas associated with attentional control in the frontal and parietal region of the brain were highly activated when the subjects performed the task which was incongruent to their cultural pattern. That is, the activity in the fronto-parietal region enhanced when East Asians had to ignore the contextual information, while similar enhancement happened for Americans when they had to incorporate the contextual information. These findings illustrate that the function of the neural mechanisms are also modulated to some extent by one's own culture. [19]

A follow-up fMRI study by Gutchess, Welsh, Boduroglu, and Park (2006) [20] confirmed the previous findings by using a rather complex stimulus, which consists of only the object pictures, object with background pictures and only the background pictures without the object. This particular study was done on East-Asian Americans and non-Asian Americans. Though the performance of both subject groups was equally good, the activity of the involved brain areas was significantly different. Non-Asian Americans had a higher activation in the object processing areas in the ventral visual cortex during the object recognition task whereas the East-Asian Americans exhibited higher activity in the left occipital and fusiform areas which are associated with perceptual analysis.

Related Research Articles

<span class="mw-page-title-main">Perception</span> Interpretation of sensory information

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, which in turn result from physical or chemical stimulation of the sensory system. Vision involves light striking the retina of the eye; smell is mediated by odor molecules; and hearing involves pressure waves.

An illusion is a distortion of the senses, which can reveal how the mind normally organizes and interprets sensory stimulation. Although illusions distort the human perception of reality, they are generally shared by most people.

<span class="mw-page-title-main">Optical illusion</span> Visually perceived images that differ from objective reality

In visual perception, an optical illusion is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect. An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.

Auditory illusions are illusions of real sound or outside stimulus. These false perceptions are the equivalent of an optical illusion: the listener hears either sounds which are not present in the stimulus, or sounds that should not be possible given the circumstance on how they were created.

<span class="mw-page-title-main">McGurk effect</span> Perceptual illusion

The McGurk effect is a perceptual phenomenon that demonstrates an interaction between hearing and vision in speech perception. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound. The visual information a person gets from seeing a person speak changes the way they hear the sound. If a person is getting poor-quality auditory information but good-quality visual information, they may be more likely to experience the McGurk effect.

<span class="mw-page-title-main">Figure–ground (perception)</span> Humans ability to separate foreground from background in visual images

Figure–ground organization is a type of perceptual grouping that is a vital necessity for recognizing objects through vision. In Gestalt psychology it is known as identifying a figure from the background. For example, black words on a printed paper are seen as the "figure", and the white sheet as the "background".

Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalities may be integrated by the nervous system. A coherent representation of objects combining modalities enables animals to have meaningful perceptual experiences. Indeed, multisensory integration is central to adaptive behavior because it allows animals to perceive a world of coherent perceptual entities. Multisensory integration also deals with how different sensory modalities interact with one another and alter each other's processing.

<span class="mw-page-title-main">Language processing in the brain</span> How humans use words to communicate

In psycholinguistics, language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the same grammatical understanding or systematicity in even human's closest primate relatives.

Subjective constancy or perceptual constancy is the perception of an object or quality as constant even though our sensation of the object changes. While the physical characteristics of an object may not change, in an attempt to deal with the external world, the human perceptual system has mechanisms that adjust to the stimulus.

The two-streams hypothesis 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 leads to the temporal lobe, which is involved with object and visual identification and recognition. The dorsal stream leads to the parietal lobe, which is involved with processing the object's spatial location relative to the viewer and with speech repetition.

Speech perception is the process by which the sounds of language are heard, interpreted, and understood. The study of speech perception is closely linked to the fields of phonology and phonetics in linguistics and cognitive psychology and perception in psychology. Research in speech perception seeks to understand how human listeners recognize speech sounds and use this information to understand spoken language. Speech perception research has applications in building computer systems that can recognize speech, in improving speech recognition for hearing- and language-impaired listeners, and in foreign-language teaching.

In psychology and neuroscience, time perception or chronoception is the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the indefinite and unfolding of events. The perceived time interval between two successive events is referred to as perceived duration. Though directly experiencing or understanding another person's perception of time is not possible, perception can be objectively studied and inferred through a number of scientific experiments. Some temporal illusions help to expose the underlying neural mechanisms of time perception.

The motor theory of speech perception is the hypothesis that people perceive spoken words by identifying the vocal tract gestures with which they are pronounced rather than by identifying the sound patterns that speech generates. It originally claimed that speech perception is done through a specialized module that is innate and human-specific. Though the idea of a module has been qualified in more recent versions of the theory, the idea remains that the role of the speech motor system is not only to produce speech articulations but also to detect them.

<span class="mw-page-title-main">Superior temporal sulcus</span> Part of the brains temporal lobe

In the human brain, the superior temporal sulcus (STS) is the sulcus separating the superior temporal gyrus from the middle temporal gyrus in the temporal lobe of the brain. A sulcus is a deep groove that curves into the largest part of the brain, the cerebrum, and a gyrus is a ridge that curves outward of the cerebrum.

The neuroscience of music is the scientific study of brain-based mechanisms involved in the cognitive processes underlying music. These behaviours include music listening, performing, composing, reading, writing, and ancillary activities. It also is increasingly concerned with the brain basis for musical aesthetics and musical emotion. Scientists working in this field may have training in cognitive neuroscience, neurology, neuroanatomy, psychology, music theory, computer science, and other relevant fields.

<span class="mw-page-title-main">Oddball paradigm</span> Psychology research paradigm

The oddball paradigm is an experimental design used within psychology research. The oddball paradigm relies on the brain's sensitivity to rare deviant stimuli presented pseudo-randomly in a series of repeated standard stimuli. The oddball paradigm has a wide selection of stimulus types, including stimuli such as sound duration, frequency, intensity, phonetic features, complex music, or speech sequences. The reaction of the participant to this "oddball" stimulus is recorded.

<span class="mw-page-title-main">Visual capture</span>

In psychology, visual capture is the dominance of vision over other sense modalities in creating a percept. In this process, the visual senses influence the other parts of the somatosensory system, to result in a perceived environment that is not congruent with the actual stimuli. Through this phenomenon, the visual system is able to disregard what other information a different sensory system is conveying, and provide a logical explanation for whatever output the environment provides. Visual capture allows one to interpret the location of sound as well as the sensation of touch without actually relying on those stimuli but rather creating an output that allows the individual to perceive a coherent environment.

Change deafness is a perceptual phenomenon that occurs when, under certain circumstances, a physical change in an auditory stimulus goes unnoticed by the listener. There is uncertainty regarding the mechanisms by which changes to auditory stimuli go undetected, though scientific research has been done to determine the levels of processing at which these consciously undetected auditory changes are actually encoded. An understanding of the mechanisms underlying change deafness could offer insight on issues such as the completeness of our representation of the auditory environment, the limitations of the auditory perceptual system, and the relationship between the auditory system and memory. The phenomenon of change deafness is thought to be related to the interactions between high and low level processes that produce conscious experiences of auditory soundscapes.

Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to half a second and is consistent with the idea that the visual system models events prior to perception.

Multistable auditory perception is a cognitive phenomenon in which certain auditory stimuli can be perceived in multiple ways. While multistable perception has been most commonly studied in the visual domain, it also has been observed in the auditory and olfactory modalities. In the olfactory domain, different scents are piped to the two nostrils, while in the auditory domain, researchers often examine the effects of binaural sequences of pure tones. Generally speaking, multistable perception has three main characteristics: exclusivity, implying that the multiple perceptions cannot simultaneously occur; randomness, indicating that the duration of perceptual phases follows a random law, and inevitability, meaning that subjects are unable to completely block out one percept indefinitely.

References

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  11. 1 2 Deutsch, D. (1991). The tritone paradox: An influence of language on music perception. Music Perception, 8(4), 335-347.
  12. ↑ "Diana Deutsch - Phantom Words".
  13. ↑ Shinn-Cunningham, B.G. (2008). "Object-based auditory and visual attention". Trends in Cognitive Sciences. 12 (5): 182–186. doi:10.1016/j.tics.2008.02.003. PMC   2699558 . PMID   18396091.
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  15. ↑ Masuda, Takahiko; Nisbett, Richard E (Nov 2001). "Attending holistically versus analytically: Comparing the context sensitivity of Japanese and Americans". Journal of Personality and Social Psychology. 81 (5): 922–934. doi:10.1037/0022-3514.81.5.922. PMID   11708567.
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