PSY 100 General Psychology
Lecture Guide 4: Consciousness
Michael L. Thomas, PhD
1 Introduction and Learning Objectives
🎥 Watch this before starting!
🎥 Watch this!
Before continuting with this lecture guide watch this YouTube video.
2 What is Consciousness?
Consciousness is your awareness of yourself and the world around you. It means being awake and able to experience things like thoughts, emotions, and sensations. It includes everything you are actively thinking or feeling—whether it’s noticing a sound, making a decision, or recalling a memory. Consciousness also refers to the part of your mental life that you are aware of, as opposed to unconscious processes that happen automatically, without your awareness. Two important aspects of consciousness are:
- Monitoring: The act of scanning your sensory and perceptual environment for specific types of information.
- Selective Attention: The process of focusing your mental and perceptual resources on one particular type or source of input while filtering out others.
🚨 Note: Not all actions are guided by conscious decisions. Right now, you are (hopefully) focusing on these words—not on earlier events, your growling stomach, background noise, or the hum of a nearby vent. But if a threat suddenly appeared—like a smoke alarm—you would immediately shift your attention to monitor the danger, and stop focusing on this text.
3 Inattentional Blindness
So let’s get back to the gorilla from the video above. About 50% of people who watch the video you previously viewed fail to notice the gorilla walking through the scene. If you missed it, don’t worry—it’s completely normal.
Inattentional blindness is the failure to notice a fully visible but unexpected stimulus when your attention is engaged on something else. Why does it happen? Because humans are remarkably good at focusing attention. When you’re given a direct instruction to attend to certain aspects of the environment, your brain selectively filters out other information. Information that is not being selectively attended to must be highly salient in order to capture your attention.
Think of it this way: at any given moment, you are bombarded with a constant stream of sensory information—sounds, sights, bodily sensations, and more. Yet even just moments later, you can recall only a tiny fraction of those details. Trying to monitor everything all the time would overwhelm your brain. So instead, your brain uses filtering mechanisms to manage the flood of input.
In fact, within the first 100–200 milliseconds of sensory processing (about one-tenth to one-fifth of a second), your brain is already suppressing some inputs and enhancing others. And here’s the exciting part: even though this filtering happens outside of your conscious awareness, you can consciously control this filtering. That is, while you did not consciously tell your brain to ignore the gorilla, you did focus your selective attention on the basketball.
But be careful—selective attention is a double-edged sword. While it helps you focus on important tasks, it can also cause you to miss unexpected but critical information. A very serious example is distracted driving. Listening to music, talking with passengers, eating, using a phone, and so on diverts your conscious attention away from driving. Numerous studies show that when attention is focused elsewhere, performance on the primary task suffers. Even if your overt visual attention (eye gaze) is on the road, your covert attention (mental focus) may be elsewhere. When that happens, you’re more likely to miss objects that are directly in front of you—as the gorilla video demonstrates.
🧠 Clinical Insight:
People diagnosed with schizophrenia often show impairments in sensory processing and attentional filtering. This means they may have difficulty distinguishing relevant from irrelevant sensory input. These challenges with basic sensory filtering likely contribute to the perceptual and cognitive difficulties that underlie functional impairments and disability in daily life.
4 Unconscious Processes
The vast majority of our mental processes occur outside of conscious awareness. This so-called unconscious has long fascinated psychologists and neuroscientists Although the concept dates back to antiquity, Austrian physician Sigmund Freud is most commonly associated with it. As we’ll explore later in the course, Freud believed that our behavior is strongly influenced by unconscious thoughts and feelings.
Examples include:
- Implicit bias: Unconscious attitudes or stereotypes that affect our understanding, decisions, and actions without us realizing it. These biases can influence behavior even when we consciously reject them.
- Subliminal perception: The processing of sensory information below the threshold of conscious awareness. For example, brief or subtle stimuli can influence thoughts or behavior without being consciously noticed.
- Automatic behaviors: Actions that occur without conscious thought or effort, usually due to habit or learned patterns. Examples include driving a familiar route without thinking about each movement.
While each of these processes has been shown to be scientifically valid, there is ongoing debate about their strength and real-world implications.
One example of this debate involves the popularized concept of a Freudian slip—the idea that people sometimes accidentally substitute words in speech that reveal their hidden intentions, concerns, or desires (e.g., saying to a sports opponent, “I’m glad to beat you” instead of “I’m glad to meet you”). However, many cognitive psychologists and linguists argue that such slips are better explained by patterns of speech production, such as phonological similarity, cognitive load, or recent word activation, rather than unconscious motivations.
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5 Biological Rhythms and Sleep
5.1 Circadian Rhythms
The human body runs on a roughly 24-hour cycle known as the circadian rhythm, regulated by the suprachiasmatic nucleus (SCN) in the hypothalamus. Any rhythmic change that continues on approximately a 24-hour cycle—even without external time cues—is considered a circadian rhythm. Examples include fluctuations in body temperature, cortisol secretion, and the sleep–wake cycle.
A key hormone, melatonin, is secreted by the pineal gland and helps regulate sleep–wake cycles. Light exposure suppresses melatonin release, which is why screen time before bed can disrupt sleep.
🌒 Did You Know?
Our biological actually runs a little slow! In complete darkness or isolation, humans drift into a natural rhythm closer to 24.2 hours, not exactly 24. Fortunately light and routines keep us on schedule.
5.2 Stages of Sleep
We can distinguish sleep stages using an electroencephalogram (EEG), which records rapid fluctuations in scalp voltage reflecting the summed postsynaptic activity of large populations of cortical pyramidal neurons beneath each electrode.
Relaxed wakefulness (eyes closed): When you’re awake but calm with eyes closed, the EEG shows alpha waves (8–12 Hz), especially over the back of the head. These rhythms fade when you open your eyes or focus hard, because the brain shifts into a more alert processing mode.
Stage N1 (Stage 1): This is the lightest stage of sleep, a brief “drifting off” period. The EEG shifts to low-amplitude, mixed frequencies with a theta tilt (~4–7 Hz). People may feel like they’re still awake, and can experience hypnagogic imagery or a sudden hypnic jerk as they nod off.
Stage N2 (Stage 2): Sleep becomes more stable. You’ll still see background theta, but two hallmark events appear: sleep spindles (~11–16 Hz bursts lasting ~0.5–2 s) that help protect sleep and support memory, and K-complexes, large waves that often occur after noises but keep you asleep. This is still considered light sleep.
Stage N3 (slow-wave sleep; sometimes previously split into Stages 3 & 4): The EEG shows large, slow delta waves (~0.5–4 Hz). This is deep sleep, when it’s hardest to wake someone and when the body does much of its physical restoration and energy replenishment.
REM sleep: The eyes dart rapidly, most muscles are atonic (temporarily paralyzed), and the EEG looks wake-like (low-amplitude, mixed frequency, including theta and some beta). Vivid dreaming is common here, and REM periods lengthen across the night as sleep cycles repeat roughly every 90 minutes.
Sleep typically cycles from N1 → N2 → N3 → back to lighter stages and then REM about every ~90 minutes, with the first REM period occurring roughly 70–110 minutes after sleep onset and lengthening across the night.
Note: 1 Hertz (Hz) = one cycle per second.
Throughout the night, our bodies cycle through all stages of sleep repeatedly. Early in the night, deep (slow-wave) sleep dominates, playing a critical role in physical restoration. In contrast, later sleep cycles contain longer REM periods, which are associated with memory consolidation, emotional processing, and brain development.
REM sleep typically accounts for about 20–25% of total sleep time. The majority of vivid dreaming occurs during REM sleep, which is associated with increased brain activity, particularly in the central nervous system. One possible explanation for why REM sleep increases later in the night is that it may help prepare the brain to awaken and re-engage with the external world.
Sleep patterns also vary with age. Newborns tend to spend about 50% of their sleep in REM sleep, while adults typically spend around 20% of their sleep in REM. In addition, older adults tend to experience significantly less Stage 3 and Stage 4 (deep) sleep, and in some individuals, these stages may disappear completely. Overall, total sleep duration decreases with age, and the structure of sleep shifts—often resulting in more fragmented and lighter sleep in older adulthood.
🌐 Explore this! Follow this link to a LEARNING EEG website that will teach you how to identify sleep by looking at EEG brainwaves. Begin with the LEARN and then see how many brainwave EEG images you can correctly classify under the PRACTICE tab.
5.3 Sleep Disorders
While the brain and endocrine system are generally adept at regulating sleep cycles, problems can arise from both behavioral choices and biological factors.
5.3.1 Sleep Deprivation
Most people need 8 to 9 hours of sleep per night to avoid signs of sleep deprivation. About 90% of people sleep between 6 and 9 hours. A common sign of sleep deprivation is feeling a temporary loss of energy, particularly in the afternoon.
Sleep researchers have shown that alertness significantly increases when individuals who normally get 8 hours of sleep are given an additional 2 hours. Sleep deprivation is associated with fatigue, difficulty concentrating, and microsleeps (e.g., falling asleep at the wheel).
Tips for better sleep include:
- Maintain a regular sleep schedule
- Limit alcohol and caffeine (especially before bedtime)
- Avoid heavy meals close to bedtime
- Exercise regularly (but not right before bed)
- Avoid sleeping pills, as they disrupt natural sleep cycles
- Minimize light exposure (including screens) before bed
- Practice relaxation techniques before sleep
🧠 Clinical Insight:
While alcohol and certain sedative drugs may initially help people fall asleep, they often lead to fragmented and lower-quality sleep. These substances disrupt the normal progression through sleep stages—especially REM sleep. This can impair both cognitive functioning and overall well-being.
5.3.2 Insomnia
Insomnia is defined as dissatisfaction with the amount or quality of sleep. Although biological causes exist, insomnia is more often the result of poor sleep habits. Interestingly, many people who claim to have insomnia actually show little disturbance on sleep recordings—perhaps only 30 minutes of wakefulness during the night. In many cases, the problem is not insomnia itself, but inconsistent or unhealthy sleep routines.
5.3.3 Narcolepsy
Narcolepsy involves recurring, irresistible attacks of drowsiness that can cause someone to fall asleep suddenly during the day. These episodes may last from a few seconds to 15–30 minutes, and may occur several times per day. Narcolepsy affects about 1 in 2,000 people.
5.3.4 Sleep Apnea
Sleep apnea occurs when a person stops breathing during sleep. It can be caused by a failure of the brain to signal the diaphragm to breathe, or by relaxed throat muscles that collapse the airway. When oxygen levels drop, the body releases emergency hormones, briefly waking the sleeper. Although many people experience brief apnea episodes, those with severe apnea may have hundreds per night. As a result, they may sleep for 12 hours and still feel tired during the day.
6 Dreams
6.1 Dreaming
Dreaming is an altered state of consciousness in which remembered images and fantasies are temporarily confused with external reality. Despite exhaustive research, we still do not fully understand why people dream or what dreams mean.
Sigmund Freud famously proposed that dreams offer a window into the unconscious mind. He believed that dreams allowed the primitive and instinctual part of the mind (i.e., the id) to express its deepest desires—wishes that are symbolically disguised to prevent disturbing the dreamer. Freud even developed a coding system to interpret these symbols. While his ideas remain culturally influential, modern research has found little scientific evidence to support Freud’s dream theory.
Although some people claim they never dream, research suggests that all people dream, but not all people remember their dreams. Whether a dream is remembered may depend on whether it is transferred from short-term memory to long-term memory (we’ll learn more about these systems later in the course) in the seconds immediately after waking.
Dream time appears to be roughly equivalent to real time. For example, if you dream of a conversation that seems to last five minutes, it likely occurred over a similar amount of actual time during sleep.
Most people are unaware that they are dreaming while it’s happening. However, some individuals experience lucid dreams, in which they are aware they are dreaming and may even control their actions or the dream environment.
There is some evidence that people can influence their dreams (e.g., by using pre-sleep suggestions), but limited evidence that people can consistently control them.
6.2 Theories of Dream Function
Researchers have proposed several theories about why we dream:
- Dreams may help consolidate or reorganize information gathered during the day.
- They may serve to process emotions, especially those tied to stress or unresolved problems.
- Some researchers argue dreams are a byproduct of random neural activation during REM sleep—essentially meaningless.
Interestingly, dream content often differs sharply from waking life:
- Violent or bizarre content is common. One study found that murder rates in dreams were about 2,226 per 100,000 dream characters—much higher than in real life.
- Negative emotions also appear frequently.
This suggests that rather than solving real-world problems, dreams may reflect a person’s underlying thoughts, concerns, and emotional preoccupations.
💤 Fun Fact:
Did you know that people can practice skills in their dreams—and actually improve in real life?
Research shows that athletes, musicians, and even surgeons who rehearse actions in their dreams (particularly lucid dreaming) may show enhanced performance when awake. Your brain’s motor regions activate during REM sleep almost as if you’re physically practicing—like a free training session while you sleep!
6.3 Neurological Processes Asscoaited with Dreaming
Dreaming typically occurs during REM sleep and involves increased brain activity, vivid internal imagery, and dominance of the neurotransmitter acetylcholine. At the same time, the brain becomes largely disconnected from the outside world and from higher-order thinking areas like the dorsolateral prefrontal cortex, which are important for self-awareness and critical thinking. During REM, the brain spontaneously pulls from memory systems—including personal experiences and general knowledge—to create immersive, emotional dream scenarios. However, we often have trouble remembering these dreams. This amnesia is linked to reduced activity in brain areas that rely on serotonin, norepinephrine, and dopamine, as well as decreased activation in prefrontal regions that normally help us form and retrieve memories.
7 Hypnosis
Hypnosis is a state in which a willing and cooperative individual relinquishes some control over their behavior to the hypnotist and accepts a temporary distortion of reality. While in a hypnotic state, individuals may:
- Stop planning and act more automatically
- Focus their attention narrowly—often only on the hypnotist’s voice
- Increase imaginative or fantasy thinking
- Experience distorted perceptions of reality
- Become more suggestible
- Exhibit temporary amnesia for certain events or instructions
Many people ask whether hypnosis is “real”. The challenge in answering this question is that we still don’t fully understand how hypnosis works. Undoubtedly, some carnival shows and entertainment acts have portrayed hypnosis in a misleading—or even harmful—light. However, hypnosis has been practiced for over 200 years, originating with Anton Mesmer in the late 1700s. While Mesmer misunderstood the mechanism (attributing it to mysterious animal magnetism), his demonstrations laid the groundwork for later scientific exploration.
One of the first to seriously study hypnosis as a medical phenomenon was Dr. Jean-Martin Charcot, a mentor to Freud. Charcot recognized that what Mesmer attributed to “magnetic forces” was more accurately explained as the power of suggestion, and he explored its use in treating patients with “hysteria” and other psychological conditions (the word hysteria comes from the Greek hystera, meaning uterus, reflecting the sexist and unscientific belief that women’s psychological distress was caused by a wandering womb.)
Today, millions of people report real benefits from clinical hypnosis, particularly in reducing psychological distress, pain, and anxiety. While hypnosis remains partially mysterious, it is widely accepted as one of many altered states of consciousness—alongside dreaming, meditation, drug use, and immersive “flow” states like becoming absorbed in a movie or task.
However, people vary in how easily they can be hypnotized. About 5–10% of the population cannot be hypnotized at all. Others may be highly susceptible, even experiencing hallucinations:
- Positive hallucinations: Seeing or hearing things that are not there
- Negative hallucinations: Failing to perceive something that is present (e.g., not feeling pain)
In clinical settings, negative hallucinations are often used to reduce pain perception during therapy.
8 Psychoactive Drugs
Psychoactive drugs affect behavior, consciousness, and mood. These include not only illegal substances but also widely used legal ones such as caffeine and nicotine.
Throughout history, different cultures have varied in their acceptance or regulation of psychoactive substances. In modern society, a major public health concern is the potential for drug abuse and dependence.
Drug abuse occurs when drug use leads to harmful consequences—such as legal trouble, job loss, or damaged relationships.
Drug dependence involves:
- Tolerance: Needing more of the substance to achieve the same effect.
- Withdrawal: Experiencing unpleasant physical or psychological symptoms when use is reduced or stopped.
- Compulsive use: Continued use despite negative consequences, often accompanied by significant time or effort spent acquiring the substance.
- Tolerance: Needing more of the substance to achieve the same effect.
Nearly all psychoactive drugs have the potential to lead to both abuse and dependence if used frequently or without caution. Some psychoactive substances also carry the risk of causing serious harm or death, even after a single use—particularly at high doses or in vulnerable individuals. Moreover, with the advent of synthetic drugs in recent decades, the risk of immediate toxic effects, overdose, and death has increased significantly due to their high potency and unpredictable composition.
The opioid crisis in the United States is a tragic and ongoing public health emergency. Beginning in the early 2000s and continuing into the 2020s, the country experienced a dramatic increase in opioid overoses and deaths. While the initial rise in fatalities was largely attributed to commonly prescribed opioids and heroin, around 2015 there was a sharp and alarming surge in overdose deaths linked to synthetic opioids—especially fentanyl and related substances—as shown in the image below.
The major categories of psychoactive drugs include the following:
Depressants reduce activity in the central nervous system (CNS). These include:
- Alcohol
- Barbiturates (e.g., Nembutal, Seconal)
- Tranquilizers (e.g., Miltown, Xanax, Valium)
- Inhalants (e.g., paint thinner, glue)
Opiods (Narcotics) reduce the perception of pain and can also suppress physical sensation and responsiveness to stimuli. While they are medically used for pain relief, they are often misused for their euphoric and sedative effects. Examples:
- Opium
- Morphine
- Codeine
- Heroin
- Fentanyl
Stimulants increase CNS activity and boost alertness, arousal, and energy by increasing monoamine neurotransmitter levels (e.g., dopamine, norepinephrine, serotonin). Examples:
- Amphetamines
- Cocaine
- Methamphetamine
- Ecstasy (MDMA)
Hallucinogens alter perceptual experiences—affecting color, sound, time perception, and potentially causing hallucinations. Examples include:
- LSD
- Psilocybin (magic mushrooms)
- Mescaline
- PCP (Phencyclidine)
Cannabis is derived from the Cannabis sativa plant. It can produce depressant, stimulant, and hallucinogenic effects, and therefore does not fit neatly into a single drug category.
- Marijuana consists of dried leaves and flowers.
- Hashish is made from the plant’s resin.
Its active ingredient, THC (tetrahydrocannabinol), produces effects including euphoria, altered time perception, and relaxation. However, it may also cause anxiety, confusion, or panic. Cannabis use can impair motor coordination and short-term memory, and studies show cognitive performance may remain impaired for up to 24 hours after use—even if users report feeling unaffected.
🌐 Watch this! Follow this link to a Khan Academy video that provides additional details about the psychoactive drugs listed above.
9 Summary
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