Consciousness, Sensation, and Perception for the MCAT: Everything You Need to Know
/Learn key MCAT concepts about consciousness, sensation, and perception, plus practice questions and answers
(Note: This guide is part of our MCAT Psychology and Sociology series.)
Table of Contents
Part 1: Introduction to consciousness, sensation, and perception
Part 2: Consciousness
a) EEGs and waveforms; beta, theta, alpha, delta, etc
b) Sleep cycles
c) Circadian rhythms
d) Consciousness-altering drugs
Part 3: Sensation
a) Sensory thresholds
b) Visual sensation
c) Auditory sensation
d) Physical sensation
e) Chemical sensation
Part 4: Perception
a) Adaptation to stimuli
b) Visual processing
c) Proprioception
Part 5: High-yield terms
Part 6: Passage-based questions and answers
Part 7: Standalone questions and answers
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Part 1: Introduction to consciousness, sensation, and perception
Psychology is the study of interactions between the mind, body, and environment. The body receives sensations from the environment, encodes them in a specific way, and sends these signals to the brain to be formed into conscious perception. The combination of multiple simultaneous sensations and perceptions leads us to a clearer understanding of the world around us.
Studying this topic for the MCAT can be very daunting as it appears to cover a lot of material. The human body has many different mechanisms of sensation and perception, and understanding each of these mechanisms is no simple task. In this guide, we will break down the main concepts you will need to know for the MCAT and will provide real-life examples similar to those you will see on exam day.
Several important terms are scattered throughout this guide and are bolded. While we provide some definitions, feel free to create your own terms, definitions, and examples that serve you best! At the end of this guide, there is an MCAT-style passage and standalone questions that will test your knowledge on these topics.
Let’s begin!
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Part 2: Consciousness
What is consciousness? Many philosophers and psychologists have drawn different conclusions in response to this question. Dualists like Rene Descartes suggest that the mind and body are two separate entities that work together to create an internal picture of the self and the environment. Physicalists believe that there is no such separate entity as the mind and that every thought, perception, and sensation that we experience is a direct result of the physical being, namely, the body and brain. Still, others believe that consciousness arises from a mix of dualism and physicalism.
Though there is much disagreement, one thing has been made clear. Consciousness is an innate and inseparable property of living beings that describes an awareness of ourselves and the environment we live in. It requires the reception of sensations from the environment, encoding these sensations into signals that travel to the brain, and decoding these signals to create an understanding of both ourselves and the surroundings.
a) EEGs & waveforms
An EEG, or electroencephalogram, is a non-invasive test that uses electrodes to detect the brain’s electrical activity and determine the active state of the brain at any given time. The brain’s neurons are constantly firing, even when we are asleep. By observing the waveforms detected by the EEG, the brain’s state of activity can be observed at any time.
There are several key waveforms that appear on a typical EEG. Each of these waveforms provides insight into what state of consciousness the brain is in.
Alpha waves are typical of an awake and resting or drowsy state. These waves show a low amplitude and high-frequency pattern.
Beta waves are typical of either an awake and alert state or REM sleep. These waves demonstrate a sawtooth pattern with low amplitude and high frequency.
Theta waves are typical of the early stages of sleep (Stage 1 & 2). These waves show a moderate amplitude and moderate frequency.
Delta waves are found in deep stages of sleep (Stage 3 & 4). These waves are characterized by large amplitude and low frequency.
Practices such as hypnosis and meditation can additionally alter these waveforms. Experienced practitioners of meditation may be able to experience theta waves during consciousness, while hypnosis can induce altered patterns of alpha waves.
b) Sleep cycles
Sleep serves many functions, including the consolidation of memory, the release of growth hormones, and the healing of injuries. While sleep clearly plays an important role in our lives, its complexities are poorly understood.
Our sleep cycle is divided into several stages. During sleep, the state of the brain cycles through a fixed pattern of waveforms. One sleep cycle lasts roughly 1.5 hours, so a night’s sleep is typically composed of 5-6 sleep cycles. Let’s take a closer look at the individual stages of the sleep cycle.
Awakeness, though technically not part of the sleep cycle itself, is characterized by beta waves. During awakeness, individuals are conscious of their surroundings and go about their daily living.
Drowsiness occurs when individuals have their eyes closed and are relaxing. This stage is characterized by alpha waves.
Stage 1 is the first stage of sleep. This stage of light sleep is characterized by theta waves. The eyes are slowly rolling, and the muscles begin to relax.
Stage 2 is also composed of theta waves and occurs when entering medium sleep. The heart rate begins to drop, breathing rate slows, and core temperature begins to fall due to changes regulated by the hypothalamus. This stage is characterized by unique EEG features called K complexes and sleep spindles, which are bursts of unique electrical activity interspersed among theta waves.
Stage 3 marks the beginning of deep sleep. In this stage, which is characterized by large slow delta waves, the heart rate continues to fall.
Stage 4 comprises the bulk of deep sleep. Characterized by delta waves, we achieve the deepest sleep in this stage. This is where the body undergoes the most repair, memory consolidation, and growth hormone release.
REM (rapid eye movement) stage occurs after Stage 4 and is characterized by the same sawtooth beta waves that are found in the awake state. REM sleep is also referred to as paradoxical sleep, in which the mind is alert but the body is motionless. During this stage, there is also quick eye movement, vivid dreams and imagery, and high electrical activity in the brain. To prevent the body from receiving the brain’s signals and acting out any harmful actions in dreams, the body’s muscles enter a temporarily paralyzed state.
During sleep, we dream. What are dreams? Some, like Freud, say that dreams are a form of “manifest content” that reveals the “latent content”—in other words, the plotlines of the dreams show insight into the deepest secrets and unconscious desires. Others believe that dreams are a way to build problem-solving skills and improve learning during REM sleep.
Yet others believe that dreams are merely byproducts of brain activity during REM. This theory is called the activation-synthesis theory, which states that dreams serve no real purpose and are simply the result of random neural activity.
This entire sleep cycle, from stage 1 through REM sleep, lasts roughly 90 minutes. As the night progresses, the deep sleep stages (stages 3 & 4) become shorter and the REM stage becomes longer and more frequent. REM frequency decreases with aging, in addition to the total hours needed for nightly sleep. REM rebound is a phenomenon that occurs when REM sleep occurs with earlier onset and longer duration—particularly when individuals experience sleep deprivation or otherwise inadequate sleep.
Sleep disorders can also affect the duration or quality of sleep that a patient receives. Insomnia refers to an inability to fall asleep that is not attributed to a relevant cause. As a result, insomnia may be considered a symptom of another psychological disorder.
Narcolepsy is a sleep disorder in which patients fall asleep and often at inappropriate times during the day. It is often associated with cataplexy, a sudden loss of muscle tone. Patients with these disorders may pose harm to themselves or others, as they are unable to control when they fall asleep and may be unable to protect themselves in dangerous situations.
Parasomnias are a group of sleep disorders that refer to abnormal behavior during, directly before, or directly after sleep. They are most commonly found in children and often spontaneously resolve by adolescence. Parasomnias include sleepwalking, night terrors, and sleep paralysis.
For more information on related disorders, be sure to refer to our guide on psychological disorders.
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