the distinct modes of vision offered by feedforward and recurrent processing victor a.f. lamme and...
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![Page 1: The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema](https://reader036.vdocuments.us/reader036/viewer/2022062313/56649d5d5503460f94a3b726/html5/thumbnails/1.jpg)
The distinct modes of vision offered by feedforward and recurrent processing Victor
A.F. Lamme and Pieter R. Roelfsema
![Page 2: The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema](https://reader036.vdocuments.us/reader036/viewer/2022062313/56649d5d5503460f94a3b726/html5/thumbnails/2.jpg)
Dichotomies in the Visual System?
• What are three dichotomies that Lamme identifies in the visual system?
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Dichotomies in the Visual System?
• What are three dichotomies that Lamme identifies in the visual system?
• Dorsal vs. Ventral stream
![Page 4: The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema](https://reader036.vdocuments.us/reader036/viewer/2022062313/56649d5d5503460f94a3b726/html5/thumbnails/4.jpg)
Dichotomies in the Visual System?
• What are three dichotomies that Lamme identifies in the visual system?
• Dorsal vs. Ventral stream
• Pre-attentive vs. Attentive
![Page 5: The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema](https://reader036.vdocuments.us/reader036/viewer/2022062313/56649d5d5503460f94a3b726/html5/thumbnails/5.jpg)
Dichotomies in the Visual System?
• What are three dichotomies that Lamme identifies in the visual system?
• Dorsal vs. Ventral stream
• Pre-attentive vs. Attentive
• Conscious vs. Unconscious
![Page 6: The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema](https://reader036.vdocuments.us/reader036/viewer/2022062313/56649d5d5503460f94a3b726/html5/thumbnails/6.jpg)
The Feed-Forward Sweep
• What is the feed-forward sweep?
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The Feed-Forward Sweep
• The feed-forward sweep is the initial response of each visual area “in turn” as information is passed to it from a “lower” area– a single spike per synapse– no time for lateral connections – no time for feedback connections
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The Feed-Forward Sweep
• The feed-forward sweep is the initial response of each visual area “in turn” as information is passed to it from a “lower” area
• Consider the latencies of the first responses in various areas
QuickTime™ and a decompressor
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The Feed-Forward Sweep
• Thus the “hierarchy” of visual areas differs depending on temporal or anatomical features
• Three aspects of the visual system account for this fact:
– Some neurons in an area don’t receive direct connections from the next “lower” area
– multiple feed-forward sweeps progressing at different rates (I.e. magno and parvo pathways) in parallel
– signals arrive at cortex via routes other than the Geniculo-striate pathway (LGN to V1)
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The Feed-Forward Sweep
• The feed-forward sweep gives rise to the “classical” receptive field properties– tuning properties exhibited in very first spikes– think of cortical neurons as “detectors” only during feed-
forward sweep
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After the Forward Sweep
• By 150 ms, virtually every visual brain area has responded to the onset of a visual stimulus
• But visual cortex neurons continue to fire for hundreds of milliseconds!
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After the Forward Sweep
• By 150 ms, virtually every visual brain area has responded to the onset of a visual stimulus
• But visual cortex neurons continue to fire for hundreds of milliseconds!
• What are they doing?
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After the Forward Sweep
• By 150 ms, virtually every visual brain area has responded to the onset of a visual stimulus
• But visual cortex neurons continue to fire for hundreds of milliseconds!
• What are they doing?
• with sufficient time (a few tens of ms) neurons begin to reflect aspects of cognition other than “detection”
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Extra-RF Influences
• One thing they seem to be doing is helping each other figure out what aspects of the entire scene each RF contains
– That is, the responses of visual neurons begin to change to reflect global rather than local features of the scene
– recurrent signals sent via feedback projections are thought to mediate these later properties
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Extra-RF Influences
• consider texture-defined boundaries– classical RF tuning
properties do not allow neuron to know if RF contains figure or background
– At progressively later latencies, the neuron response differently depending on whether it is encoding boundaries, surfaces, the background, etc.
QuickTime™ and a decompressor
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Recurrent Signals in Object Perception
• Can a neuron represent whether or not its receptive field is on part of an attended object?
• What if attention is initially directed to a different part of the object?
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Recurrent Signals in Object Perception
• Can a neuron represent whether or not its receptive field is on part of an attended object?
• What if attention is initially directed to a different part of the object?
Yes, but not during the feed-forward sweep
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Recurrent Signals in Object Perception
• curve tracing– monkey indicates whether a
particular segment is on a particular curve
– requires attention to scan the curve and “select” all segments that belong together
– that is: make a representation of the entire curve
– takes time
QuickTime™ and a decompressor
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Recurrent Signals in Object Perception
• curve tracing– neuron begins to respond
differently at about 200 ms
– enhanced firing rate if neuron is on the attended curve
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Feedback Signals and the binding problem
• What is the binding problem?
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Feedback Signals and the binding problem
• What is the binding problem?• curve tracing and the binding problem:
– if all neurons with RFs over the attended curve spike faster/at a specific frequency/in synchrony, this might be the binding signal
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Feedback Signals and the binding problem
• What is the binding problem?• curve tracing and the binding problem:
– if all neurons with RFs over the attended curve spike faster/at a specific frequency/in synchrony, this might be the binding signal
But attention is supposed to solve the binding problem, right?
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Feedback Signals and the binding problem
• So what’s the connection between Attention and Recurrent Signals?
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Feedback Signals and Attention
• One theory is that attention (attentive processing) entails the establishing of recurrent “loops”
• This explains why attentive processing takes time - feed-forward sweep is insufficient
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Feedback Signals and Attention
• Instruction cues (for exaple in the Posner Cue-Target paradigm) may cause feedback signal prior to stimulus onset (thus prior to feed-forward sweep)
• think of this as pre-setting the system for the upcoming stimulus
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Feedback Signals and Attention
• We’ll consider the role of feedback signals in attention in more detail as we discuss the neuroscience of attention