From 6971be657e3eacf302e1918b6480ee07be10abca Mon Sep 17 00:00:00 2001 From: maalaria Date: Mon, 14 Jan 2019 21:27:52 +0100 Subject: [PATCH] face selectivity update --- .../face_selectivity.tex | 53 ++++++++++--------- 1 file changed, 27 insertions(+), 26 deletions(-) diff --git a/projects/project_face_selectivity/face_selectivity.tex b/projects/project_face_selectivity/face_selectivity.tex index 512c5aa..b7b9a54 100644 --- a/projects/project_face_selectivity/face_selectivity.tex +++ b/projects/project_face_selectivity/face_selectivity.tex @@ -11,7 +11,7 @@ %%%%%%%%%%%%%% Questions %%%%%%%%%%%%%%%%%%%%%%%%% -\section{Estimating the face-selectivity index (FSI) of neurons} +\section{Estimating the selectivity index (SI) of neurons} In the temporal lobe of primates you can find neurons that respond @@ -26,7 +26,7 @@ stimulus the newborn typically sees is the mother's face. It is believed that the early ubiquity of faces and their importance for social interactions triggers the development of the so called face-patch system within the temporal lobe of primates.\par Your task -here will be to estimate the \textit{face selectivity index} ($FSI$) +here will be to estimate the \textit{selectivity index} ($SI$) of neurons that were recorded in the superior temporal sulcus of a rhesus monkey during the visual presentation of objects of different categories (data courtesy of the Sensorymotor-Lab, Hertie @@ -50,14 +50,14 @@ Institute). \begin{parts} \part - Illustrate the spiking activity of all neurons, sorted by object + Illustrate the spiking activity of 10 neurons, sorted by object category, in a raster plot. As a result you should get one plot for each neuron subdevided in subplots for the different categories. Mind that there are four categories that contain faces (\texttt{averted\_human}, \texttt{face} (straight human face), \texttt{monkey} (straight monkey face) and \texttt{gaze\_monkey}), - you may want to analyze them separately as well combined. Add also - a marker where the stimulus starts. + you may want to analyze them separately as well as combined. Add + also a marker where the stimulus starts. \part Estimate the time-resolved firing rate of each neuron for each @@ -65,13 +65,14 @@ Institute). (e.g. instantaneous firing rate based on interspike intervals, spike counting within bins (PSTH), kernel density estimation). Do this individually for each trial and average afterwards in order - to obtain the standard deviation of the firing rates. Plot the - firing rates and their standard deviations on top of the raster - plots. Which of the methods appears best to represent - the spiking activity seen in the raster plots? + to obtain the standard deviation of the firing rates. For the 10 + neurons that you plotted above plot the firing rates and their + standard deviations on top of the raster plots. Which of the + methods appears best to represent the spiking activity seen in the + raster plots? \part - Generate figures that show for each neuron the firing rates + Generate a figure that shows for 20 neurons the firing rates belonging to each object category. Don't forget to add an appropriate legend. @@ -80,46 +81,46 @@ Institute). modulations. % First, normalize each response to baseline activity % (first 400 ms). Why is the normalization useful? - % \par Now, determine the periods within which the neurons - activity deviates from the baseline activity at least by - $2*\sigma$. Do this for each object category and mark the periods - in the plots in an appropriate way. Are there neurons that do not - repond to the visual stimulation or exhibit inhibitory responses? + Determine the periods within which the neurons activity deviates + from the baseline activity at least by $2*\sigma$. Do this for + each object category and mark the periods in the plots in an + appropriate way. Are there neurons that do not respond to the + visual stimulation or exhibit inhibitory responses? \par \part - The $FSI$ gives an estimate of how strongly a neuron is tuned to + The $SI$ gives an estimate of how strongly a neuron is tuned to the chosen object categories. It is given by the neuron's response - during the presentation of the one category compared to the other + during the presentation of one category compared to another category. \begin{equation} SI = \frac{ \mu_{\text{Response to category A}} - \mu_{ \text{Response to category B}} } { \mu_{\text{Response to category A}} + \mu_{ \text{Response to category B} } } \end{equation} - $FSI$ can take values between -1 and 1 which indicates tuning to + $SI$ can take values between -1 and 1 which indicates tuning to the one or to the other category. There are different possibilities of how it can be estimated. The easiest way would be to average the spike count during the whole time of stimulus presentation. However, if responses are phasic you will - underestimate the $FSI$. Therefore, you should limit the estimate + underestimate the $SI$. Therefore, you should limit the estimate to periods of significant modulations. Use the periods determined - in (d). Store all obtained $FSI$s within a single variable. We are - mainly interested in identifying face-selective neurons but feel - free to test the neurons for selectivity to other categories, as - well. + in (d). Why may using the value of the peak activity be inappropriate? + Store all obtained $SI$s within a single variable. We are mainly + interested in identifying face-selective neurons but feel free to + test the neurons for selectivity to other categories, as well. \part - Plot the distribution of $FSI$ values and describe it + Plot the distribution of $SI$ values and describe it qualitatively. Does it indicate a continuum or a distinct population of face-selective neurons. \par Think about a statistical test that tells you whether a given neuron is significantly modulated by one or the other category (try different combinations of categories). List cells that show significant modulations to faces and non-faces. Which is the - minimum $FSI$ that reaches significance when choosing $\alpha = - 0.05$? Is it an all or nothing selectivity? + minimum $SI$ that reaches significance when choosing + $\alpha = 0.05$? Is it an all or nothing selectivity? \part Take a look at the time resolved firing rates of the identified