Visual Inattention – Gorillas in Our Midst and How Magic Tricks Work

 

A Level Psychology

Visual Inattention – Gorillas in Our Midst and How Magic Tricks Work

One of the most famous studies in psychology is Simons and Chabris’ “Gorillas in Our Midst”.
In this experiment, participants watched a video of people passing a basketball and were asked to count the passes. Half of the viewers failed to notice a person in a full gorilla suit walking across the screen.

This striking demonstration shows inattentional blindness — the failure to see something obvious when attention is focused elsewhere.
It’s not a flaw in our eyes, but a limitation of our cognitive attention system.

This same psychological principle explains why magicians can make objects disappear, switch items unnoticed, or produce illusions that seem impossible. Magic works because our brains prioritise, filter, and ignore far more than we realise.

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What Is Inattentional Blindness?

Inattentional blindness happens when:

• attention is focused on a demanding task,

• the unexpected event is unrelated to that task, and

• the person has no reason to expect anything unusual.

The gorilla walking across the screen is visible to the eyes but invisible to attention.

This phenomenon tells us that perception is active, not passive. We don’t see the world fully — we see what we are paying attention to.

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Why Do So Many People Miss the Gorilla?

Psychology research shows several factors increase inattentional blindness:

1. High cognitive load

When mental effort is focused on counting, solving, or tracking, fewer resources remain for noticing the unexpected.

2. Expectations

People expect only basketball-related events. A gorilla simply isn’t anticipated.

3. Expertise and familiarity

Those familiar with selective attention tasks, such as elite sports players, are sometimes more likely to notice unusual stimuli — or sometimes less likely, depending on what they focus on.

4. Change blindness links

Even when looking directly at something, rapid or unexpected changes often go unnoticed.

Magicians use all of these factors to their advantage.

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How Magic Tricks Exploit Inattentional Blindness

Illusionists understand attention better than most psychologists. Many magic effects rely on:

1. Misdirection

The magician draws your attention to the right hand, while the left hand performs the method.
Your eyes may see it — your attention does not.

2. Expectation violation

If an object has behaved consistently throughout the trick, your brain stops monitoring it closely.
This makes it perfect for a switch or disappearance.

3. Cognitive overload

Fast movements, patter, humour, noise, or a sudden surprise occupy working memory, leaving fewer resources to notice the deception.

4. Attentional “bottlenecks”

The brain cannot consciously process everything at once.
Magicians create moments where only one interpretation seems possible — and hide the real method just outside the spotlight of attention.

Students recognise how the same cognitive limitations that hide the gorilla also hide the secret of a magic trick.

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Why This Topic Works in A Level Psychology

Inattentional blindness links directly to:

• selective attention

• cognitive load

• perception and information processing

• real-world consequences (driving, eyewitness testimony, health and safety)

• applications in advertising, sports, and UX design

It shows students that what we think we saw may not match what actually happened — a key theme in cognitive psychology.

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Skills Highlight

• Evaluating Simons & Chabris (method, validity, ethics, conclusions)

• Linking attention theories to everyday behaviour

• Analysing real-world failures of perception

• Understanding how attention can be manipulated

 

Understanding Encryption – Writing a Caesar Cipher in Python

Encryption is at the heart of modern cybersecurity — from messaging apps to online banking. Students often imagine encryption as something complex and mysterious, but many key ideas begin with surprisingly simple methods. One of the earliest examples is the Caesar cipher, used by Julius Caesar to send secure messages to his generals.

Writing a Caesar cipher in Python is an excellent introduction to encryption at GCSE and A Level Computing. It helps students understand substitution ciphers, modular arithmetic, character encoding, and the logic behind more advanced systems.

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What Is a Caesar Cipher?

A Caesar cipher shifts each letter in a message by a fixed number of positions in the alphabet.
For example, with a shift of 3:

• A → D

• B → E

• C → F

The message “HELLO” becomes “KHOOR”.

It’s simple, but it introduces students to two key ideas:

• Encryption (scrambling a message)

• Decryption (undoing the scrambling)

Modern encryption is vastly more complex — but the logic of substitution and key-based security begins here.

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Writing a Caesar Cipher in Python

Here is a simple encryption function:

def caesar_encrypt(text, shift):
    result = ""
    for char in text:
        if char.isalpha():
            base = ord('A') if char.isupper() else ord('a')
            result += chr((ord(char) - base + shift) % 26 + base)
        else:
            result += char
    return result

And a matching decryption function:

def caesar_decrypt(cipher, shift):
    return caesar_encrypt(cipher, -shift)

Students can test their program:

message = "Secret Message"
encrypted = caesar_encrypt(message, 4)
decrypted = caesar_decrypt(encrypted, 4)

This shows encryption and decryption clearly and logically.

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Extending the Task

More confident students can:

• Add support for punctuation and numbers

• Create a brute-force attack to test all 26 possible shifts

• Analyse letter frequencies to understand why the cipher is weak

• Link this to modern encryption and hashing algorithms

This builds understanding of cybersecurity, algorithm design, and ethical hacking.

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Why It Works in Teaching

Students gain experience in:

• String manipulation

• Loops and conditionals

• Character encoding (ASCII/Unicode)

• Modulus arithmetic

• Thinking like both a programmer and an attacker

Most importantly, they see that encryption is not magic — it’s a series of logical steps designed to hide information.

 

Testing Water Quality – Hardness and pH

GCSE Chemistry

Water may look clean, but its chemical properties vary widely depending on geology, treatment, and environmental factors. Two of the most important measures students learn at GCSE are water hardness and pH. These tests show how dissolved ions affect everyday life — from limescale in kettles to how soap lathers in hard or soft water.

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What Is Hard Water?

Hard water contains dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
These ions come from rocks such as limestone, chalk, and dolomite as rainwater slowly dissolves them.

Hardness affects:

• how well soap lathers

• the formation of limescale

• water taste

• efficiency of kettles, boilers, and washing machines

Testing hardness gives students a direct link between chemistry and household science.

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The Soap Solution Test (GCSE Core Practical)

Equipment:

• Water samples (tap water, bottled water, distilled water, rainwater, river water, pond water, seawater)

• Standard soap solution

• Conical flasks

• Measuring cylinder

Method:

1. Place 10 cm³ of water into the flask.

2. Add soap solution a few cm³ at a time, shaking well.

3. Measure how much soap is needed to form a stable lather for 10 seconds.

4. Repeat for each water sample.

Interpretation:

• More soap needed → harder water

• Less soap needed → softer water

This test works because Ca²⁺ and Mg²⁺ ions react with soap to form scum, reducing lather.

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Testing pH

pH tells us how acidic or alkaline water is. Most drinking water is pH 6.5–8.5, depending on treatment and natural minerals.

Methods:

• pH paper (quick, approximate)

• Universal indicator (colour scale)

• Digital pH sensor (accurate, ideal for A-level or more precise investigation)

Causes of variation:

• Dissolved carbon dioxide

• Natural mineral content

• Pollution or acid rain

• Water treatment chemicals (e.g. chlorine)

Students can compare pH values across water sources and relate differences to geology and human activity.

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Typical Classroom Results

Water Sample	Soap Added for Lather (cm³)	Hardness	pH
Distilled water	1–2	Very soft	~7
Local tap water	4–6	Moderately hard	7.5
Bottled spring water	6–8	Hard	7
Rainwater	1–2	Soft	5.5–6 (slightly acidic)

Students immediately see why some regions suffer from limescale — and why rainwater can be acidic despite looking clean.

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Skills Highlight

• Performing fair comparative tests

• Measuring and recording pH values

• Interpreting data from qualitative and quantitative methods

• Understanding ions in solution and their effects on everyday life

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Why It Works in Teaching

These tests connect GCSE Chemistry directly to real life. Students recognise the science behind household appliances, water treatment, soap use, and environmental issues — making the topic both relevant and memorable.

 

Simple Harmonic Motion – Measuring SHM with PASCO Sensors

Simple Harmonic Motion (SHM) appears all over physics: oscillating springs, swinging pendulums, vibrating masses, tuning forks, air columns, and even molecules in solids. It’s a perfect topic for hands-on investigation, and with PASCO sensors, students can collect precise displacement, velocity, and acceleration data to see SHM unfold in real time.

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What Is Simple Harmonic Motion?

An object in SHM experiences a restoring force that is proportional to its displacement and acts towards equilibrium:

$$F = -kx$$

This produces motion that is:

• periodic,

• symmetrical,

• and modelled by sine and cosine functions.

PASCO equipment makes these ideas visible and measurable.

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Measuring SHM with PASCO Sensors

1. Spring–Mass System (Wireless Motion Sensor or Smart Cart)

Attach a mass to a vertical or horizontal spring.
Start oscillations and use the motion sensor to track displacement.

Data shows:

• sinusoidal displacement–time graphs

• velocity 90° out of phase

• acceleration proportional to –displacement

Students calculate the period:

$$T = 2\pi \sqrt{\frac{m}{k}}$$

and verify it experimentally.

Add the Force Sensor to see the effect of force.

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2. Simple Pendulum (Motion Sensor or Photogate)

A PASCO rotational sensor or a motion sensor or photogate can track the oscillation period of a small pendulum.
Students test how the period changes with:

• length of the string

• amplitude (for small angles)

and compare data with:

$$T = 2\pi\sqrt{\frac{L}{g}}$$

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3. Smart Cart Oscillations on a Track

The PASCO Smart Cart, acting as a mass attached to long springs, provides a clean horizontal SHM system. The Pasco Track is mounted at a steep angle, and the cart is allowed to oscillate, suspended by a spring.

With the track level two, springs can be used, one at the top and the other at the bottom.
Built-in position and acceleration sensors allow simultaneous measurement of:

• $x(t)$

• $v(t)$

• $a(t)$

Graphs clearly show the phase relationships between each.

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4. Torsional Oscillator (Rotary Motion Sensor)

Using a rotary motion sensor and a torsion wire, students observe rotational SHM.
They can measure moment of inertia, torsion constant, and compare with:

$$T = 2\pi\sqrt{\frac{I}{k_\tau}}$$

This links SHM theory to rotational dynamics.

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Why PASCO Makes SHM Clear

• Real-time graphs reveal phase differences instantly

• Data is smooth and accurate, ideal for curve fitting

• Students can test how mass, stiffness, and amplitude affect period

• Results link directly to A Level equations and modelling

The combination of hands-on systems and digital sensors helps students understand SHM as both a physical motion and a mathematical model.

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Skills Highlight

• Collecting and analysing real-time motion data

• Using PASCO sensors to measure displacement, velocity, and acceleration

• Fitting sinusoidal curves to experimental data

• Investigating how system parameters affect oscillation

• Linking mathematical models to physical behaviour

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Why It Works in Teaching

SHM is everywhere — from clocks and guitars to earthquakes and resonance.
PASCO technology lets students see the full picture:
the forces, the curves, the timing, and the mathematics behind oscillatory systems.

 

Exploring Correlation – Do Taller People Have Bigger Feet?

Correlation is one of the first statistical ideas students meet at GCSE and A Level, and it’s much easier to understand when linked to real-world data. One of the simplest — and most popular — classroom investigations asks a surprisingly sensible question:

Do taller people have bigger feet?

It’s a fun way to explore data collection, scatter graphs, line of best fit, and the difference between correlation and causation.

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The Investigation

Students work in pairs or groups to collect two sets of data:

• Height (in cm)

• Foot length (in cm or shoe size converted to cm for accuracy)

Measurements are plotted on a scatter graph, with height on the x-axis and foot size on the y-axis.

A line of best fit allows students to see whether a pattern exists — and in most cases, the answer is yes. Taller people tend to have longer feet.

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What Students Discover

1. Correlation, Not Causation

A positive correlation does not mean one variable causes the other. Height doesn’t cause big feet, and big feet don’t cause height — both are linked by underlying factors such as genetics and growth.

2. Strength of Correlation

Students calculate or estimate:

• Weak correlation

• Moderate correlation

• Strong correlation

• Very strong correlation

Real biological variation means the points never fall perfectly on the line.

3. Outliers Matter

Some individuals don’t follow the general pattern. Discussing why — genetics, age differences, measurement error — helps students think critically about real data.

4. Regression Line Interpretation

The line of best fit helps predict approximate values, but with caution. Prediction inside the data range (interpolation) is reasonable; outside it (extrapolation) becomes unreliable.

Yes, taller people generally have larger feet because there is a positive correlation between height and foot size. However, this relationship is not absolute, as genetics, nutrition, age, and sex also influence foot size, leading to individual variation. Some taller people have average-sized feet, while some shorter people have large feet. 

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Classroom Skills Developed

• Collecting measurable, reliable data

• Plotting accurate scatter graphs

• Drawing and interpreting lines of best fit

• Understanding correlation coefficients

• Evaluating outliers and data reliability

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Why It Works in Teaching

Students enjoy this investigation because it’s personal, measurable, and immediately meaningful.
The data isn’t abstract — it comes from them.

This makes the statistical concepts far easier to grasp and shows how correlation helps scientists, medics, economists, and businesses understand patterns in the world.

 

Measuring the Speed of Sound with a Tuning Fork and a Tube

Measuring the speed of sound doesn’t need specialist lab equipment. A simple tuning fork, a resonance tube, and a beaker of water allow students to determine the speed of sound in air with impressive accuracy. This classic physics experiment links frequency, wavelength, and resonance — all central ideas in waves and acoustics.

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The Experiment

Equipment:

• Tuning forks of known frequency (e.g. 256 Hz, 320 Hz)

• Hollow resonance tube or a cardboard/plastic tube

• Large beaker or cylinder of water

• Metre ruler

Method:

1. Fill the beaker with water and place the tube vertically inside so that the bottom end is submerged.

2. Strike the tuning fork and hold it just above the top of the tube.

3. Slowly raise the tube to change its effective air column length.

4. At a certain point, the tube will resonate — the sound becomes much louder.

5. Measure the length of the air column at this point.

6. Use this length to estimate the wavelength of the sound.

Why does this work?
The tube acts as a pipe closed at one end (the water surface). The first resonance occurs when the air column is one quarter of the wavelength:

$$L = \frac{\lambda}{4}$$

So:

$$\lambda = 4L$$

Once the wavelength is known:

$$v = f\lambda$$

where

• $v$ = speed of sound

• $f$ = frequency of tuning fork

• $\lambda$ = wavelength

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Typical Results

For a 256 Hz tuning fork:

• Resonance length measured: 33 cm (0.33 m)

• Estimated wavelength:

  $$\lambda = 4 \times 0.33 = 1.32\text{ m}$$
  

• Speed of sound:

  $$v = 256 \times 1.32 \approx 338\text{ m/s}$$
  

This is very close to the accepted value of around 343 m/s at room temperature.

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Why It Works in Teaching

This method gives a loud, unmistakable resonance that makes wavelength and frequency feel real.
Students hear the physics, measure the physics, and calculate the speed of sound themselves.

It’s ideal for linking experimental method with wave theory, resonance, and the relationship $v = f\lambda$.

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Skills Highlight

• Identifying resonance experimentally

• Measuring air column lengths accurately

• Calculating wavelength and wave speed

• Understanding closed-pipe harmonics

 

Tracking Populations – Sampling and Quadrat Studies

Can This Be Done in the Winter Months?

Sampling with quadrats is one of the most important ecological fieldwork techniques used at GCSE and A Level Biology. It allows students to estimate population size, distribution, and biodiversity without counting every organism in an area. But what happens in winter, when plants die back and animals are harder to spot?

The good news is that population sampling can still be carried out effectively in winter — as long as you adapt your methods.

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The Basics of Quadrat Sampling

Quadrat studies involve placing a square frame (usually 0.25 m² or 1 m²) on the ground and recording:

• Species present

• Number of individuals

• Percentage cover

• Frequency

Students use random sampling for unbiased population estimates, or systematic sampling (belt transects) to study how communities change across a gradient — such as shade to light or wet to dry ground.

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Can You Do This in Winter?

Yes — with some limitations and adaptations.

1. Plant Species

Many perennial plants survive winter below ground, so above-ground shoots may be reduced. However:

• Evergreen species (holly, ivy, mosses, grasses) remain visible

• Many plants leave identifiable structures (stems, basal rosettes)

• Mosses and lichens are often easier to sample in winter because they aren’t shaded by summer growth

• Tree seedlings and saplings can still be counted

Winter sampling gives an accurate picture of overwintering plant communities, which is valid ecological data in its own right.

2. Invertebrates and Animals

These are harder to observe in winter, but not impossible:

• Leaf litter sampling reveals beetles, worms, springtails, and centipedes

• Pitfall traps still work, though activity is lower

• Evidence such as burrows, droppings, tracks, and feeding marks can be recorded

Winter studies shift focus from abundance to distribution and habitat use.

3. Abiotic Factors Matter More

In winter, quadrat work pairs well with measuring:

• Soil temperature

• Light intensity

• Soil pH

• Moisture content

This helps students understand how winter conditions influence survival and distribution.

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Why Winter Sampling Is Valuable

• Shows how ecosystems change seasonally

• Highlights adaptations to cold, low-light conditions

• Teaches students to collect valid data even in difficult conditions

• Provides contrasting results to compare with spring/summer sampling

• Encourages resilience and fieldwork skills

Winter ecology is real science: conservation volunteers, ecologists, and environmental agencies work outdoors year-round.

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Skills Highlight

• Random and systematic sampling

• Identifying species (including overwintering forms)

• Calculating population density, frequency, and percentage cover

• Understanding seasonal effects on ecosystems

• Working safely and efficiently in cold-weather fieldwork