Stimuli and Human Perception

Introduction

From the time of birth and every day in our lives, human beings are faced with different kinds of stimuli. A variety of stimuli is sensed by different organs in the human body. This is due to the existence of nerves which send impulses to the brain for the sake of comprehension in order to send back impulses, which result in response – it is biological. Therefore, stimuli are converted to sensations throughout the human body, which are interpreted by the brain. Interpretation results in the comprehension of the stimuli. There are different kinds of stimuli, and they include heat, cold, pain, and pleasure, among others. The process by which stimulus is interpreted by the brain is known as perception (Sharma, 2009).

This essay aims at defining perception and describing how the top-down and bottom-up approaches have explained perception. The essay shall begin by presenting the different definitions of perception in order to create understanding from different points of view. Then, the top-down and bottom-up approaches will be described to provide a focused procedural description of perception.

Perception allows the human brain to understand what stimuli is. From the above description, it can be deduced that perception involves two processes, and they are sensation and interpretation. Although it is important to understand that interpretation relies on past experience. For instance, a young child who has never seen a wolf either on direct eye contact or from an image, will not be able to identify the animal as being a wolf, and in another case, a child who has seen the wolf in either means can easily place an identity to it (Sharma, 2009). Therefore, perception can be defined as the process where the present stimulus is interpreted according to previous experience (Bodenhausen & Hugenberg, 2007).

Taking a trip down history will reveal how perception among the modern world human beings was shaped by the experiences of early hominids – the ancestors to the current generation of people. Fundamentally, the human mind is programmed to successfully navigate challenges which relate to reproduction and survival. Generally, it can be articulated that central to acquiring success in challenging situations is the mental operations in the human brain. The mental operations result in the recognition of threats, opportunities, and the development of the right strategies to either avoiding or exploiting them. Although early hominid minds may be fundamentally preoccupied with the recognition of dangerous predators and substances which are edible, the contemporary human mind mainly focuses on different kinds of concerns such a philosophy, entertainment and science which have a little direct linkage to the concerns of reproduction and survival (Bodenhausen & Hugenberg, 2007).

The utmost social nature of the human race is the key behind the comparatively rich capacities of cognition among people. Early hominids are typified by high degrees of sociality, and while living in interdependency among groups, they grow the ability to understand the minds of members in that group. In order to understand other people’s minds, it is crucial to perceive and attend to every available cue, whether non-verbal or verbal, which consist of information about the inner qualities of others. Therefore, the study of perception grew out of the understanding of social cognition, which focuses on the ability of the perceiver to analyze the traits and states (such as the emotional state) of other people. Therefore, the cognitive representations of different actors and the different contexts in which they exhibit certain behavior mediate a person’s behavioral response to the social realm. The cognitive representations introduce meaning to the sensory inputs which are received and, in turn, they result in corresponding responses. Simply put, thinking is meant to trigger a responsive action which models behavior. Therefore, with this understanding, perception is regarded as the interface between the inner and outer worlds (Bodenhausen & Hugenberg, 2007).

Kant worked on a more nuanced and richer overview of defining perception, and this is evident by the manner in which he communicates about the nature of pictorial representations, the way they connect to human imagination and their essence in perception. In his book Critique of Pure Reason, Kant posits that imagination is an ingredient which is necessary for perception. Therefore, it can be understood that an image is a perceptual representation. Kant links perception with imagination because he believes that senses do not only invoke abstract impressions but also combines them together in our minds, eventually producing images of physical objects. He challenges the empiricist beliefs that receptive sensible abilities produce images in mind by adding that there is ‘something more’ to it, and this ‘something more’ is the synthetic process of imagination. Generally, Kant insists that imagination plays a primary role, and its impact on the formation of abstract images in mind results in perception (Matherine, 2015).

To provide a snapshot, in order to better understand Kant’s rich definition of perception, a phenomenological view shall be given. This phenomenological view shall dwell on the sensible faculty of cognition – the faculty which is responsible for the representations which the human mind has of objects throughout time as they interact with them. The sensible representations are delineated into two classifications, the ‘given-‘ and the ‘made-’ representations (Matherine, 2015). The given-representations, according to Kant, are the representations of the sense, and they exist passively in the human mind as they interact with objects. The made-representations are those who are imitated from the senses (Matherine, 2015). Given-representations exist passively in the senses of the human mind, while made-representations require that people interact with something physically in order to accord sense to them. Kant introduces the ‘formative power,’ which grants the human mind the ability to develop these kinds of representations. The formative power is a substitute name for imagination. Therefore, the formative power facilitates perception through mundane activities such as remembering the past, making anticipations of the future and perceiving the world as it is around a person (Matherine, 2015).

The top-down approach to understanding perception, which is also known as the conceptual-driven or the knowledge-driven process, is directed by the expectations which are acquired from previous learning or contexts, or both. Put differently, top-down processes of perception are controlled by stored knowledge. Top-down processing involves the use of contextual knowledge that is acquired from human memory, which is known as the ‘big picture.’ Therefore, this approach focuses on information which already exists within one’s neural system.

The effects of context in perception are tested in the effort of viewers trying to identify certain objects in certain scenes in the real world. Both time length and accuracy are important in the efforts to recognize the objects, and they vary from one context to another. For instance, in a scene where a kitchen is depicted, it is easier for viewers to identify objects like utensils or food, and it is way more difficult to identify such objects in a similar scene where everything is jumbled. This example leads to psychologists using the top-down approach to argue that for any model of perception to work, expectations and contexts ought to be incorporated (Galotti, 2013).

Another example is where an individual is asked to identify a fly in a dark room and observe the first place where the individual would look out for the fly. Noticeably, the direction of the individual’s glance would change if they were asked to identify a cockroach or a spider in the same dark room. The processing that occurs when the individual is looking at the specific locations of the darkroom for the spider or cockroach can be regarded as top-down processes. The top-down approach interacts with the bottom-up approach, or else, it would be difficult to perceive anything which is not in expectation, and one would only perceive what they are expected to perceive.

One of the top-down processes which incorporate bottom-up approaches is that of David Marr. The model suggested by Marr is mathematically elegant and quite technical. According to Marr, perception occurs in term of a number of different computational mechanisms which have a special purpose, like a module which analyzes color, and another module which analyzes colour. Each computational mechanism operates independently without any input support from another module and does not consider the knowledge of the real world. Therefore, they are bottom-up procedures (Galotti, 2013, p. 52).

Marr posits that three separate mental representations are necessary for the process of visual perception. These mental representations are the primal sketch, a two-and-a-half-dimensional sketch, and the three-dimensional sketch (3D sketch) (Demuth, 2012). The primal sketch and the two-and-a-half-dimensional sketch are largely exclusively bottom-up processes. The primal sketch is like a two-dimensional representation which depicts the relative regions of darkness and brightness in a geometric structure that is localized. The two-and-a-half-dimensional representation is created after the primal sketch using cues like edges, texture, shading among others and from it, the viewer can derive the kinds of surfaces in view and their positioning from their vantage point (Demuth, 2012). The 3-D representation incorporates top-down knowledge with the primal sketch and two-and-a-half-dimensional representations (bottom-up processes) – merging real-world expectations and knowledge in the formation of the final 3-D version of the visual scene. The 3-D sketch brings about recognition of the objects and their essence in creating meaning to the visual scene.

The bottom-up processing of perception relies solely on external stimuli. This approach to perception is also known as the stimulus-driven or the data-driven processing, and it begins with the trait features of the stimulus, such as the pieces and bits of stimuli (Demuth, 2012). This process is initiated by the image which reaches the retina. Then, the information is processed in a hierarchical manner by the higher degrees of the visual system in succession up to the top-most levels. Once the top-most part of the system is reached, the object gets perceived (Cherry, 2019). It is generally suggested that the bottom-up approach depends on information as it is acquired from a stimulus moving all the way up to the highest point of the neural system for processing (Shea, 2013).

This approach of perception requires that energy is taken in from the surrounding and converted to neural signals through a process called sensation. Bottom-up processing can be exemplified in a classroom where students are seated on desks arranged in a row. The student on the final seat of the row begins the process by writing down a word on a page of a notebook, tears the page and hands the piece of paper to the next student in front of them. The next student writes down more information (probably another word, or provides an illustration), then, they hand the paper to the student in front of them who adds more content. The process repeats in a subsequent manner until the student at the front of the row is reached. The students present at the front position of the row are denied the chance to request the students at the rear position of the row to clarify the information presented in the piece of paper (Galotti, 2013).

Psychologists using the bottom-up approach consider information from stimuli as being input. The processes in the bottom-up are independent of the information acquired from previous learning or experience. The bottom-up processes are automatic and reflexive, and they take place when the viewer is passively taking in information. One process that is related to the bottom-up approach is that of feature analysis (Galotti, 2013). Feature analysis involves analyzing a whole unit into smaller parts, and this is the fundamental process of perception. Rather than processing stimuli as whole units, the viewer breaks them down, thus viewing them according to their components or features. Therefore, under feature analysis, in order to place recognition of a whole object, its features ought to be recognized first. For instance, when looking at a dog as a whole unit, a viewer can break down the object into component parts and consider the features such as the fur color, fur length, shape of ears and color of the snout (Galotti, 2013).

Conclusion

In conclusion, there exist several thinkers who have attempted to define perception. Although the definitions may be different, they all have a common ground – the reference that perception arises from the interpretation of stimuli. Perception is part of human nature, and since everyone has separate minds and independent thoughts, different things are perceived differently by different people. Kant’s definition of perception communicates about the nature of pictorial representations in the human mind, the way they connect to human imagination and their essence in perception. The top-down approach is conceptual-driven. It is contextual knowledge that is acquired from human memory, which is known as the ‘big picture.’ The bottom-up approach to defining perception is stimulus-driven. It depends on information as it is acquired from a stimulus moving all the way up to the highest point of the neural system for processing. Knowing the different ways of defining perception, as well as the top-down and bottom-up approaches to explaining perception is key in cognitive psychology. It aids in understanding and being able to predict how different people process information from the environment.

References

• Bodenhausen, G. & Hugenberg, K., 2007. Attention, Perception, and Social Cognition.
• Cherry, K., 2019. How Bottom-Up Processing Works. [Online] Available at: https://www.verywellmind.com/bottom-up-processing-and-perception-4584296
• Demuth, A., 2012. Perception Theories. Krakow: ResearchGate.
• Galotti, K., 2013. Perception : Recognizing Patterns and Objects. In: Cognitive Psychology In and Out of The Laboratory: Sage Publishers, pp. 55-64.
• Matherine, S., 2015. Images And Kant's Theory of Perception. Journal of Philosophy, 2(29).
• Sharma, A., 2009. Perception: Meaning, Definition, Principles, and Factors Affecting in Perception. [Online] Available at: http://www.psychologydiscussion.net/perception/perception-meaning-definition-principles-and-factors-affecting-in-perception/634
• Shea, N., 2013. Distinguishing Top-Down From Bottom-Up Effects. In: Perception and Its Modalities. pp. 2-10.