24th October 2023

Principles of Visual and Auditory Perception

What is perception?

Perception relates to a stimulation of the body’s senses, which relates to our understanding of the world around us. It has been debated whether this is able to be clearly separated from memory (Peterson and Skow-Grant, 2003).

Perceptual organisation

Figure-ground differentiation

Figure-ground differentiation is where two shapes share a common border, and one of the shapes is considered to have been shaped by that border whilst the other is less defined. This concept demonstrates that visual input is organised into shapes by our brains; for example, perceiving a certain object as the focus or foreground (Peterson and Skow-Grant, 2003). Optical illusions show this phenomenon, such as Rubin’s Vase (see below), which depicts a black and white design of two faces and a vase. We will either perceive the faces or the vase, whilst the alternate image becomes less prominent. The debate regarding whether memory is needed for figure-ground differentiation stems from how we can identify these objects. Do we need to access our memories of similar images, or can we bypass this by using certain cues, for example, symmetry and area? (Peterson and Skow-Grant, 2003).

Image Source: Wikimedia Commons (2007). Cup or faces paradox, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Cup_or_faces_paradox.svg (Accessed on: 17 October 2023).

Object constancy

When we move around an object, we can still recognise it.

Object constancy proposes a way that we can recognise an object from a number of viewpoints. For example, even if we first view a teapot from the side, we can still recognise that it is a teapot from the front. Some theories suggest that we achieve this by mentally rotating the object to a more familiar orientation (viewer-centred theories), whereas others suggest that the mental representation of the object is complete enough that the viewpoint is not relevant (object-centred theories) (Turnbull et al, 1997).

Recent studies have attempted to identify which region of the brain is involved in this phenomenon. For example, a behavioural study by Nestmann et al (2021) compared stroke patients to a control group and identified that those with lesions of the right fusiform gyrus had more difficulty identifying objects from atypical views. Combined with complimentary fMRI results, they concluded that fusiform and lateral-occipital areas of the brain are important for visual object constancy.

Set

Alport (1955) discussed some of the major theories of perception and described a set as: ‘A perceptual bias or predisposition or readiness to perceive particular features of a stimulus’. An example of this would be overlooking the presence of a cat in an image which had been anticipated to contain only dogs, i.e. ignoring stimuli that do not fit with the perceptual set. Similarly, Gorbunova (2016) described a phenomenon where a person is more likely to identify similar targets once the first has been found but is hindered from finding targets with different characteristics.

Set perception has interesting applications in social psychology, as it can influence or bias our interpretation of a person’s actions and contributions. It can also be applied to certain mental illnesses. For example, obsessive-compulsive disorder (OCD) can involve overfocused attention on irrelevant or harmful stimuli (Okasha et al, 2000). There have also been studies considering the role of set perception in schizophrenia. In contrast to OCD, it appears that people with schizophrenia are less likely to fixate their attention. However, this includes missing contextual information, so it has the potential disadvantage of being less able to draw information from their social environment (Green et al, 2008).

Illusions and hallucinations

Illusions and hallucinations are misrepresentations of reality, which can be generated by pathologies in neurology, ophthalmology and psychiatry. An example of an illusion would be misperceiving a sock as a rat in a darkened room, whereas a hallucination would be visualising a rat even though there is nothing there (Norton and Corbett, 2000). Hallucinations conflict with our definition of perception, as the senses are stimulated without an external cause. Hallucinations can occur in a range of senses, such as visual, auditory or tactile, and can present in both children and adults (Jardri et al, 2014). Hallucinations may occur as a result of psychotic mental illnesses but can also present during periods of heightened stress and anxiety. Likewise, illusions may occur during states of anxiety (Jardri et al 2014). However, the diagnosis of visual perceptual abnormalities must also consider broader causes, ranging from delirium to migraines. Therefore, it is important to consider the broader context of the patient and other symptoms which they present with (Norton and Corbett, 2000).

References

• Allport, F (1955) Theories of perception and the concept of structure: A review and critical analysis with an introduction to a dynamic-structural theory of behavior. John Wiley & Sons Inc. Available at: https://doi.org/10.1037/11116-000.
• Gorbunova, E. (2016). The role of perceptual similarity in visual search for multiple targets. Journal of Vision. 173, pp. 46-54. Available at: https://doi.org/10.1016/j.actpsy.2016.11.010.
• Green, M. et al. (2008). Visual processing of social context during mental state perception in schizophrenia. 33(1), pp. 34-42. PMID: 18197270.
• Ittelson, W. (1960). Visual Space Perception. Springer.
• Jardri, R. et al (2014). From Phenomenology to Neurophysiological Understanding of Hallucinations in Children and Adolescents. Schizophrenia bulletin. 40(Suppl 4). S221-S232. Available at: http://dx.doi.org/10.1093/schbul/sbu029.
• Nestmann, S. et al (2021). The role of posterior ventral stream areas for viewpoint-invariant object recognition. Neuroimage. 251(119021). Available at: https://doi.org/10.1016/j.neuroimage.2022.119021.
• Norton, J. Corbett, J. (2000). Visual Perceptual Abnormalities: Hallucinations and Illusions. Seminars in Neurology. 20(1). pp. 111-121. Available at: https://doi.org/ 10.1055/s-2000-6837.
• Okasha, A. et al. (2000). Cognitive dysfunction in obsessive-compulsive disorder. Acta Psychiatr Scand. 101(4), pp. 281-5. PMID: 10782547.
• Peterson, M. Skow-Grant, E. (2003). Memory and Learning in Figure–Ground Perception. Psychology of Learning and Motivation. Psychology of Learning and Motivation. 42, pp. 1-35. Available at: https://doi.org/10.1016/S0079-7421(03)01001-6.
• Turnbull, O. Carey, D. McCarthy, R. (1997). The Neuropsychology of Object Constancy. Journal of the International Neuropsychological Society. 3(3), pp. 288-98. PMID: 9161108.