L1. Intro to Perception

Course Administration

• Subject: PSYC236 – Cognition & Perception

• Lecturer / Coordinator: Dr Ozgur Karakale (email for subject-level questions)

• Other Lecturers: Steve Palmisano, Mark Schira, Tim Byron

• Tutors: William, Joel, Mark, plus Ozgur in some classes
  • Tutorials start Week 2; no tutorials in Week 1
  • Each tutor will advise preferred communication method next week

• Content for each week (slides, readings, extra videos) is released every Friday for the following week via Moodle

• Two required textbooks; weekly chapter list posted on Moodle; supplementary readings uploaded as needed

• Learning support: university writing & study advisers; slides with contact details will be posted

Course Structure & Weekly Topics

• Week 1 – Introduction; physiology of the visual system (current lecture)

• Week 2 – Size & Depth Perception (Steve) + Quiz 1

• Week 3 – Colour Perception (Mark)

• Week 4 – Motion Perception (Mark) + Quiz 2

• Week 5 – Object & Face Recognition + Quiz 3; data collection for lab report in tutorials

• Week 6 – Research / Study Week (no lecture)

• Week 7 – Face Perception (Ozgur) + Quiz 4

• Weeks 8-11 – Higher-level cognition topics: attention, memory, autobiographical memory, language, cognitive biases
  • Quiz schedule continues; each quiz always covers “latest un-assessed” material (e.g., Quiz 2 = Weeks 3 & 4)

• Week 12 – Revision & wrap-up (no quiz)

Assessments Overview (3 Components)

• 8 Online Quizzes (best 7 counted)
  • 8\times2.5\% = 20\% total
  • Open-book; 5 MCQs × 12 min; window: Fri morning → Sat 23:30
  • Miss 1 quiz → replaced by mean of other 7; miss >1 without consideration → zeros (may incur technical fail)

• Lab Report (30 %)
  • Experiment run in Week 5 tutorials; collated results provided Week 8
  • 4-week write-up period; limited AI use allowed (no AI-generated un-credited text) – see subject outline

• Final Exam (50 %)
  • Closed-book; MCQ + 4 short-answer questions
  • SAQs drawn from a pool of 24 weekly questions (2 per week; prepare throughout semester)

Key Study Tips & Expectations

• Technical content can feel dense; allocate ≈12 hrs/week (lectures, tutorials, readings, revision)

• Minimise distractions; regular review makes quizzes & lab report easier

• Make use of learning advisers, lecturer/tutor emails, and Moodle resources

• "Make time now, save time later" – cumulative nature of quizzes/exam

Perception vs Cognition Fundamentals

• Sensation: raw detection (e.g., photons on retina)

• Transduction: conversion of physical energy → neural signal (e.g., light → electro-chemical)

• Perception: brain’s interpretation of sensory input

• Cognition: umbrella term for mental processes (attention, memory, reasoning, emotion) that provide top-down guidance to perception

• Five traditional senses: sight, hearing, smell, taste, touch – each with dedicated receptors and cortical areas

Top–Down vs Bottom–Up Processing: Demonstrations

• Number/Letter Figure: “12 13 14” vs “A B C” – identical middle glyph read as 13 or B depending on context

• Arcimboldo “vegetable bowl” → upright = bowl; inverted = face (bias toward face detection)

• Hollow-mask illusion: concave interior still perceived as convex face; face templates override depth cues

• "Spot-the-Dog" cloud image: once outlined, impossible to un-see – memory alters subsequent perception

Common Visual Illusions & What They Illustrate

• Hermann Grid: grey smudges at peripheral intersections – receptive-field inhibition

• Hering Illusion: straight red lines appear bowed – depth cues from radial background

• Rotating Snakes / Moving Circles: illusory motion from microsaccades

• Checker-Shadow (Adelson): squares A and B physically identical luminance; perceived differently via context & shadow

• Café Wall & Müller-Lyer: size/angle context distorts length & parallelism judgments

Visual System Anatomy: Eye

• Light path: cornea → aqueous humour → pupil (iris controls diameter) → lens (accommodation) → vitreous humour → retina

• Lens issues (refractive errors) corrected by glasses, contacts, or surgery

• Pupil reflex: bright light → constriction; dim light → dilation (lets more photons in)

Photoreceptors: Cones vs Rods

• Divergence vs Convergence:
  • Cones maintain separate channels → sharp acuity
  • Many rods pool → increased sensitivity, decreased detail

• Blind Spot: optic disc (~15° temporal to fixation); no receptors because ganglion cell axons exit eye

• Octopus/cephalopod eyes have photoreceptors facing the light, so no blind spot (illustrates inverted vertebrate retina)

Visual Angle & Retinal Image Size

• Visual angle \theta depends on object height h and distance d:
  \theta = 2\arctan\left(\frac{h}{2d}\right)

• Halving d doubles \theta → image covers twice the retinal area → stimulates more photoreceptors → greater detail

• Despite changing retinal size, perceived size remains constant (size constancy) using depth cues and top-down knowledge

Visual Pathways: Retina → LGN → V1

1. Retinal Ganglion Cell axons bundle as optic nerve

2. Partial decussation at optic chiasm
   • Nasal hemiretina fibres cross; temporal fibres stay ipsilateral

3. Post-chiasm fibres = optic tract → Lateral Geniculate Nucleus (LGN) of thalamus

4. LGN → optic radiations → Primary Visual Cortex (V1/Striate cortex) in occipital lobe

5. From V1, two major streams:
   • Ventral “What” (V4 etc.) – colour & object identity
   • Dorsal “Where/How” (V5/MT etc.) – motion & spatial location

Lateral Geniculate Nucleus (LGN)

• 6 layered structure per hemisphere
  • Layers 1-2: Magnocellular (M) – motion, flicker
  • Layers 3-6: Parvocellular (P) – colour (red/green), fine detail
  • Thin inter-laminar Koniocellular (K) slabs – blue/yellow & alerting signals

• Layer eye-segregation: each layer receives monocular input (e.g., Layer 1 right-eye, Layer 2 left-eye) enabling later binocular integration

Receptive Fields & Centre–Surround Antagonism

• RGC & LGN cells exhibit on-centre/off-surround or off-centre/on-surround organisation

• Function: enhance contrast & highlight edges / boundaries / luminance changes

• Example response logic:
  • Light only in excitatory centre → many spikes
  • Uniform illumination centre+surround → excitation ≈ inhibition → baseline firing
  • Light only in inhibitory surround → suppressed firing

Lesion Sites & Resulting Visual Field Deficits

(Central/foveal input projects bilaterally, explaining macular sparing.)

Key Terminology Reference

• Photopic vs Scotopic vision;

• Transduction, Divergence, Convergence;

• Visual Angle, Size Constancy;

• Magnocellular / Parvocellular / Koniocellular;

• On-centre / Off-centre receptive fields;

• V1 (Primary Visual Cortex), V4 (ventral/"what"), V5 (= MT, dorsal/"where");

• Optic nerve → chiasm → tract → LGN → radiations → V1

Ethical & Practical Notes

• AI tools permitted for lab report only in limited, transparent ways (no ghost-writing) – see outline

• Collaboration on weekly SAQs encouraged, but answers must be written individually to avoid academic misconduct

Quick-Fire Self-Check Questions

1. Why is reading difficult under scotopic (rod-mediated) conditions?
   • Cones (needed for acuity & colour) are inactive; rods converge heavily → low resolution.

2. Which LGN layers carry blue–yellow opponency?
   • Koniocellular layers (inter-laminar zones).

3. Formula for visual angle? \theta = 2\arctan\left(\frac{h}{2d}\right)

4. Damage to left optic tract produces loss in which field?
   • Right visual hemifield of both eyes.

End of Week 1 study notes – ensure you can sketch the visual pathway and explain at least two illusions.