NEUR1020 Chap.4 Receptive Fields and Visual Pathways
Receptive Fields and Visual Pathways
Visual information is coded through spatially organised responses and routed according to visual field. The chapter explains centre surround receptive fields, increasing receptive field size away from fixation, the selective crossing at the optic chiasm, opposite hemisphere representation and the feature hierarchy that reaches primary visual cortex.
Retinotopic maps preserve spatial neighbourhoods, while blindsight demonstrates that visually guided sensitivity can remain without ordinary conscious vision. Pathway questions are solved from the missing field backward rather than by guessing a structure name. Preserved behaviours then refine the inference by showing which information or alternative route still contributes after damage.
What this chapter covers
- 01
Centre surround receptive field coding
- 02
Pooling, eccentricity and visual acuity
- 03
Selective crossing at the optic chiasm
- 04
V1 feature selectivity and hierarchy
- 05
Retinotopy, lesions and blindsight
Worked example · free
Localising a shared visual field loss
- +1The deficit is organised by visual field across both eyes, so it is likely after the optic chiasm.
- +1Left visual field information is grouped into pathways that reach the right hemisphere.
- +1A right post chiasm pathway or right visual cortex lesion therefore fits the stated pattern.
Key terms
- Receptive field
- A receptive field is the region where stimulation changes a neuron's response.
- Optic chiasm
- The optic chiasm is the crossing point that reorganises visual signals by visual field.
- Retinotopy
- Retinotopy preserves neighbouring visual locations as neighbouring neural representations.
- Blindsight
- Blindsight is residual visual sensitivity without ordinary conscious vision in an affected field.
Receptive Fields and Visual Pathways FAQ
What does a centre surround receptive field code?
It emphasises local contrast. An on centre, off surround cell responds strongly when light favours the centre relative to the surround and less strongly to uniform illumination. The antagonistic zones therefore encode spatial differences rather than behaving as a simple light detector.
Why does each hemisphere represent the opposite visual field?
Signals from corresponding retinal halves are selectively crossed and uncrossed at the optic chiasm. This arrangement combines left field information from both eyes in right hemisphere pathways and right field information in left hemisphere pathways.
What does blindsight demonstrate?
Blindsight shows that visual information can guide forced choice or orienting behaviour when ordinary conscious vision is absent in the affected region. It supports multiple routes for visual influence, but above chance performance does not prove that normal rich visual experience remains.
Why does uniform light produce a weak centre surround response?
Uniform illumination activates antagonistic centre and surround regions together, so their effects partly cancel. The cell is more informative about a local contrast or boundary than about absolute light spread evenly across the receptive field.
How does eccentricity affect visual detail?
Receptive fields generally become larger away from fixation and pool information over a wider retinal region. That pooling supports sensitivity but reduces precise localisation of small differences, so fine spatial detail is strongest in central vision.
What is the quickest route to lesion localisation?
First classify the deficit as eye specific or visual field specific. Eye specific loss suggests a site before field information is regrouped, while the same field loss across both eyes points after the chiasm toward the opposite hemisphere.
Does blindsight imply hidden normal vision?
No. Above chance localisation shows that some visual information influences behaviour without ordinary reported vision. The evidence supports residual sensitivity through remaining routes, not a claim that conscious visual experience is intact but concealed.
What does retinotopy preserve?
Retinotopy preserves neighbourhood relations from visual space in an orderly neural map. It is not a tiny internal picture; it is a systematic arrangement that links stimulus position, cortical activity and location-specific loss after damage.
Why are V1 responses called selective?
Different V1 cells respond most strongly to particular orientations, positions or directions. Their selectivity reflects combinations of earlier inputs and begins a hierarchy in which response properties become more complex across processing stages.
How do receptive fields relate to boundaries?
Antagonistic centre and surround zones respond differently when illumination changes across space. A boundary creates unequal stimulation across those zones, often producing a stronger response than uniform light and making local contrast prominent in the neural code.
Exam move
Draw the optic chiasm route until you can derive hemisphere from visual field without a mnemonic. Then practise centre surround predictions by changing one region at a time. For lesion items, list what is missing and what is preserved before localising the damage. For blindsight, keep residual behavioural sensitivity separate from ordinary conscious seeing.
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