In the movie I, Robot, one particular robot stood out. Sonny was different. He did not simply stick to his programming; he displayed emotional intelligence that other robots could not. Sonny desired one thing that he could never have — to feel.
He could see and hear, but Sonny could not experience pain, taste ice cream, or smell the sweetness of a candle. The intricate and advanced sensory and perceptual processing that humans have is extraordinary and sets us apart.
- What is sensory processing?
- What is perceptual processing?
- What are the stages of perceptual processing?
- How do sensory and perceptual processes work?
Sensory and Perceptual Processing
Without our senses, our brain does not have access to the outside world. Sensory processing allows the brain to receive external and internal stimuli. Perceptual processing, however, allows the brain to interpret the stimuli that have been received.
Sensory Processes
You have probably heard of the five primary senses: taste, smell, vision, touch, and hearing. However, these are not the only types of sensory input that the brain receives. Other sensory information the brain may receive could include balance and body position, blood monitoring, and immune system monitoring. Even the sense of touch has subdivisions such as pain or temperature.
Fg. 1 There are five primary senses: sight, taste, smell, touch, hearing, freepik.com
To receive the stimuli, we have several receptors that respond to them. These receptors include the following:
Chemoreceptors (chemical stimuli)
Thermoreceptors (temperature changes)
Mechanoreceptors (mechanical stimuli, i.e., movement)
Photoreceptors (variations in light)
Baroreceptors (pressure changes)
The sensory processing transforms the stimuli we receive into a language that the brain can understand.
First, the brain receptors receive a stimulus. Then, through a process called transduction, the properties of the stimulus are translated into nerve impulses. After this, special detectors analyze the features of the stimulus and transform them into neural representation. The brain then accesses the information that has been previously stored and compares it to the neural representation it has received. Finally, once the brain finds a "match", it can recognize and interpret the stimulus, thus beginning the perceptual process.
Sensory Processing Examples
Here are some examples of sensory processing before reaching the perceptual process.
- You place your hand on a hot stove and feel pain.
You feel hot while in a hot tub.
You light a candle and smell its scent.
You take a bite of spoiled food, and it tastes bitter.
Perceptual Processes
Once the stimulus information has undergone the stages of sensory processing, and is now in a form the brain can understand, interpretation begins. This process is called the perceptual process. There are two ways a stimulus can be perceived — bottom-up and top-down processing.
Bottom-up processing is the most basic form of processing and is primarily data-driven.
Bottom-up processing is when the brain relies on sensory information to perceive and understand the world.
For example, once the brain receives the sensory information that makes up the letter k, the brain is generally not required to do any higher mental processing to perceive that letter as long as the person has learned how to read. Bottom-up processing usually occurs in real time. Sometimes, however, a higher level of mental processing is required for the brain to perceive sensory information. In this case, top-down processing is needed.
Top-down processing is when the brain uses a higher level of mental processing from our previous experiences and expectations to understand and perceive new stimuli.
During top-down processing, the brain cannot simply rely on the sensory information for interpretation, but must use contextual clues. These clues can include other sensory information, past experiences, motivations, emotions, and cultural perspectives.
Perceptual Process Stages
There are five stages of the perceptual process.
1) Stimulation - the sensory information is received.
2) Organization - the brain uses past experiences to form connections to familiar ideas and concepts. Ideas and patterns are being arranged as the brain begins to understand what is happening.
3) Interpretation/Evaluation - biases, emotions, motivations, and environment begin to shape our interpretation of the information received, and we begin to assign meaning to it. Interpretation is subjective and will be different for everyone.
4) Memory - our brain stores the event or moment into either our short-term or long-term memory.
5) Recall - the information that we receive can trigger past events and moments in our brain and even recover stored memories without us realizing it.
Fg. 2 Perceptual process stages, StudySmarter Original
Difference Between Sensory and Perceptual Processes
| Sensory Processes | Perceptual Processes |
|---|
| Raw data is provided | Forms our experiences |
Process during which sensory organs receive information | Process during which the brain is provided with and interprets sensory information |
Awareness of stimuli | Interpretation of stimuli |
Objective | Objective and subjective |
Sensation ends where perception begins | Perception begins where sensation ends |
Doesn't always result in perception | Always built from sensation |
Limits of Sensitivity in Sensory And Perceptual Processing
Not all stimuli around us will go through sensory processing. There is a minimum amount of energy that must be emitted by every stimulus to be detected.
The absolute threshold refers to the minimum amount of energy from a stimulus that must be emitted to be detected half of the time.
For example, what is the dimmest light or softest sound that can still be detected 50 percent of the time? Another theory, however, suggests that whether a signal is detected at all can depend on more subjective factors.
Signal Detection Theory suggests that the detection of stimuli can depend on factors such as motivation, past experiences, or expectations.
Have you ever been waiting for a text? You could swear you saw your phone light up every two minutes, only to discover you still hadn't received that message. Your expectations at this moment have led you to imagine stimuli that did not exist. Or, a mother can be awoken by the faintest murmur from her newborn but can sleep through loud construction. Signal detection theory suggests these occurrences are due to past experiences, expectations, or motivations.
Some of the stimuli below the absolute threshold can still be received but are outside our conscious awareness. These are referred to as subliminal stimuli or subliminal messages. While these messages are sensed, they do not go far enough to undergo perceptual processing, and therefore, we are unaware of them. Other times, after a stimulus has been detected, we may experience sensory adaptation and become less sensitive to that stimulus over time. For example, our eyes adjust to a dark room over time.
Sensory adaptation is the phenomenon in which sensitivity to a constant stimulus diminishes over time.
Similar to the minimum amount required to detect a stimulus, there is also a minimum amount of variation needed to detect a change or difference between two stimuli. This is referred to as the difference threshold. For example, if you are in a dark room and your phone screen lights up. It would be quite easy to detect that light. However, if you were in a bright, well-lit room, it would be much more difficult to see the brightness of the screen.
Ernst Weber took this concept one step further and found a specific ratio required to determine the difference threshold for each of our senses.
Weber's Law states that for each of the various senses, two senses must differ by a minimum ratio for a person to detect a difference.
What Occurs during Visual Sensory and Perceptual Processing?
Like any other sensory stimuli, the visual stimuli are received through receptor cells. These cells are the rods and cones. Once the rods receive the visual information, the light energy sparks chemical changes that jump-start neural signals in bipolar cells. Nerves in ganglion cells are then activated, and their axons form the strands of the optic nerve. The information briefly stops in the thalamus but eventually reaches the visual cortex located at the back of the brain in the occipital lobe. Once the visual cortex receives information, perceptual processing can begin.
Fg. 3 The eye receives visual stimuli through its receptors, Pixabay.com
Vision Perceptual Processing
The brain employs several tactics to process the visual stimuli it has received. For example, feature detectors are nerve cells in the visual cortex that recognize specific features of a stimulus, such as its edges, angles, color, depth, or movements. This feature allows us to recognize facial features. Or, in response to visual stimuli, the brain may engage in parallel processing.
Parallel processing is when the brain breaks down visual information into parts (motion, form, depth, color) and assigns them to different areas of the brain to be processed all at once.
Parallel processing explains a phenomenon called blindsight. Patients who suffered damage might report not seeing or consciously experiencing any visual stimuli, but can respond to it or report it later (Shareie et al., 2010). Also, damage in other brain areas employed during parallel processing can lead to other consequences, such as loss in the ability to detect motion or recognize faces.
Sensory and Perceptual Processing - Key takeaways
- Transduction is the process in which the properties of the stimulus are translated into nerve impulses.
- Bottom-up processing is when the brain relies on the sensory information it receives to perceive and understand the world.
- Top-down processing is when the brain uses a higher level of mental processing from our previous experiences and expectations to understand and perceive new stimuli.
- The five perceptual processing stages are: Stimulation, organization, interpretation/evaluation, memory, recall.
- The absolute threshold refers to the minimum amount of energy from a stimulus that must be emitted to be detected half of the time.
- Weber's Law states that for each of the various senses, two senses must differ by a minimum ratio for a person to detect a difference.
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