160 likes | 246 Views
Your Test. Email crystal.ehresman@uleth.ca to go over your test in person See me if you have to complain about something. Extra-RF Influences. consider texture-defined boundaries classical RF tuning properties do not allow neuron to know if RF contains figure or background
E N D
Your Test • Email crystal.ehresman@uleth.ca to go over your test in person • See me if you have to complain about something
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 responds differently depending on whether it is encoding boundaries, surfaces, the background, etc.
Extra-RF Influences • How do these data contradict the notion of a “classical” receptive field?
Extra-RF Influences • How do these data contradict the notion of a “classical” receptive field? • Remember that for a classical receptive field (i.e. feature detector): • If the neuron’s preferred stimulus is present in the receptive field, the neuron should fire a stereotypical burst of APs • If the neuron is firing a burst of APs, its preferred stimulus must be present in the receptive field
Extra-RF Influences • How do these data contradict the notion of a “classical” receptive field? • Remember that for a classical receptive field (i.e. feature detector): • If the neuron’s preferred stimulus is present in the receptive field, the neuron should fire a stereotypical burst of APs • If the neuron is firing a burst of APs, its preferred stimulus must be present in the receptive field
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?
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
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
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
Feedback Signals and the binding problem • What is the binding problem?
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
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?
Feedback Signals and the binding problem • So what’s the connection between Attention and Recurrent Signals?
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
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
Feedback Signals and Attention • We’ll consider the role of feedback signals in attention in more detail as we discuss the neuroscience of attention