The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema

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<ul><li> Slide 1 </li> <li> The distinct modes of vision offered by feedforward and recurrent processing Victor A.F. Lamme and Pieter R. Roelfsema </li> <li> Slide 2 </li> <li> Dichotomies in the Visual System? What are three dichotomies that Lamme identifies in the visual system? </li> <li> Slide 3 </li> <li> Dichotomies in the Visual System? What are three dichotomies that Lamme identifies in the visual system? Dorsal vs. Ventral stream </li> <li> Slide 4 </li> <li> Dichotomies in the Visual System? What are three dichotomies that Lamme identifies in the visual system? Dorsal vs. Ventral stream Pre-attentive vs. Attentive </li> <li> Slide 5 </li> <li> 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 </li> <li> Slide 6 </li> <li> The Feed-Forward Sweep What is the feed-forward sweep? </li> <li> Slide 7 </li> <li> 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 </li> <li> Slide 8 </li> <li> 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 </li> <li> Slide 9 </li> <li> 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 dont 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) </li> <li> Slide 10 </li> <li> 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 </li> <li> Slide 11 </li> <li> 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! </li> <li> Slide 12 </li> <li> 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? </li> <li> Slide 13 </li> <li> 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 </li> <li> Slide 14 </li> <li> 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 </li> <li> Slide 15 </li> <li> 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. </li> <li> Slide 16 </li> <li> 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? </li> <li> Slide 17 </li> <li> 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 </li> <li> Slide 18 </li> <li> 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 </li> <li> Slide 19 </li> <li> 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 </li> <li> Slide 20 </li> <li> Feedback Signals and the binding problem What is the binding problem? </li> <li> Slide 21 </li> <li> 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 </li> <li> Slide 22 </li> <li> 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? </li> <li> Slide 23 </li> <li> Feedback Signals and the binding problem So whats the connection between Attention and Recurrent Signals? </li> <li> Slide 24 </li> <li> 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 </li> <li> Slide 25 </li> <li> 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 </li> <li> Slide 26 </li> <li> Feedback Signals and Attention Well consider the role of feedback signals in attention in more detail as we discuss the neuroscience of attention </li> </ul>