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Jan Grewe 2019-01-14 18:16:46 +01:00
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projects
project_face_selectivity
face_selectivity.tex
project_pca_natural_images
pca_natural_images.tex

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projects/project_face_selectivity/face_selectivity.tex
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@ -16,20 +16,21 @@
In the temporal lobe of primates you can find neurons that respond In the temporal lobe of primates you can find neurons that respond
selectively to a certain type of object category. You may have heard selectively to a certain type of object category. You may have heard
stories about the famous grandmother neurons which are supposed to about the famous grandmother neuron which is supposed to respond
respond exclusively when the subject perceives a particular exclusively when the subject sees a particular person, i.e. the
person. Even though the existence of a grandmother neuron in the grandmother. Even though the existence of a grandmother neuron in the
strict sense is implausible, the concept exemplifies the observation strict sense is implausible, the concept exemplifies the observation
that sensory neurons within the ventral visual stream are tuned to that sensory neurons within the ventral visual stream are tuned to
certain stimuli types. One of the most important and first visual certain stimulus types. One of the most important and first visual
stimulus the newborn typically perceives is the mother's face. It is stimulus the newborn typically sees is the mother's face. It is
believed that the early ubiquity of faces and their importance for believed that the early ubiquity of faces and their importance for
social interactions triggers the development of the so called social interactions triggers the development of the so called
face-patch system within the temporal lobe of primates.\par face-patch system within the temporal lobe of primates.\par Your task
Your task here will be to estimate the \textit{selectivity index} here will be to estimate the \textit{face selectivity index} ($FSI$)
($SI$) of neurons that were recorded in the superior temporal sulcus of neurons that were recorded in the superior temporal sulcus of a
of a rhesus monkey during the visual presentation of objects of different rhesus monkey during the visual presentation of objects of different
categories. categories (data courtesy of the Sensorymotor-Lab, Hertie
Institute).
\begin{questions} \begin{questions}
@ -66,8 +67,8 @@ categories.
this individually for each trial and average afterwards in order this individually for each trial and average afterwards in order
to obtain the standard deviation of the firing rates. Plot the to obtain the standard deviation of the firing rates. Plot the
firing rates and their standard deviations on top of the raster firing rates and their standard deviations on top of the raster
plots. Which of the methods appears to be a better representation plots. Which of the methods appears best to represent
of the spike rasters? the spiking activity seen in the raster plots?
\part \part
Generate figures that show for each neuron the firing rates Generate figures that show for each neuron the firing rates
@ -79,17 +80,17 @@ categories.
modulations. modulations.
% First, normalize each response to baseline activity % First, normalize each response to baseline activity
% (first 400 ms). Why is the normalization useful? % (first 400 ms). Why is the normalization useful?
% \par % \par Now, determine the periods within which the neurons
Now, determine the periods within which the neurons activity activity deviates from the baseline activity at least by
deviates from the baseline activity at least by $2*\sigma$. Do $2*\sigma$. Do this for each object category and mark the periods
this for each object category and mark the periods in the plots in in the plots in an appropriate way. Are there neurons that do not
an appropriate way. Are there also neurons that do not repond to repond to the visual stimulation or exhibit inhibitory responses?
the visual stimulation or exhibit inhibitory responses? \par \par
\part \part
The $SI$ gives an estimate of how strong a neuron is tuned to the The $FSI$ gives an estimate of how strongly a neuron is tuned to
chosen object categories. It is given by the neurons response 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 the one category compared to the other
category. category.
\begin{equation} \begin{equation}
@ -97,33 +98,34 @@ categories.
to category B}} } { \mu_{\text{Response to category A}} + \mu_{ \text{Response to category B}} } { \mu_{\text{Response to category A}} + \mu_{ \text{Response
to category B} } } to category B} } }
\end{equation} \end{equation}
$SI$ can take values between -1 and 1 which indicates tuning to $FSI$ can take values between -1 and 1 which indicates tuning to
the one or to the other category. There are different the one or to the other category. There are different
possibilities of how it can be estimated. The easiest way would be possibilities of how it can be estimated. The easiest way would be
to average the spike count during the whole time of stimulus to average the spike count during the whole time of stimulus
presentation. However, if responses are phasic you will presentation. However, if responses are phasic you will
underestimate the $SI$. Therefor, you should limit the estimate to underestimate the $FSI$. Therefore, you should limit the estimate
periods of significant modulations. Use the periods determined in to periods of significant modulations. Use the periods determined
(d). Store all obtained $SI$s within one variable. We are mainly in (d). Store all obtained $FSI$s within a single variable. We are
interested to identify face-selective neurons but feel free to mainly interested in identifying face-selective neurons but feel
test the neurons for selectivity to other categories, as well. free to test the neurons for selectivity to other categories, as
well.
\part \part
Plot the distribution of $SI$ values and describe it Plot the distribution of $FSI$ values and describe it
qualitatively. Does it indicate a continuum or a distinct qualitatively. Does it indicate a continuum or a distinct
population of face-selective neurons. \par population of face-selective neurons. \par Think about a
Think about a statistical test that tells you whether a given statistical test that tells you whether a given neuron is
neuron is significantly modulated by one or the other category significantly modulated by one or the other category (try
(try different combinations of categories). List cells that show different combinations of categories). List cells that show
significant modulation to faces and non-faces. Which is the significant modulations to faces and non-faces. Which is the
minimum SI that reaches significance when choosing minimum $FSI$ that reaches significance when choosing $\alpha =
$\alpha = 0.05$? Is it an all or nothing selectivity? 0.05$? Is it an all or nothing selectivity?
\part \part
Take a look at the time resolved firing rates of the identified Take a look at the time resolved firing rates of the identified
face-selective neurons and examine their response properties. What face-selective neurons and examine their response properties. What
is their response-latency (choose an appropriate visualisation), are their response-latencies (choose an appropriate
is their response phasic or tonic. visualisation), are their responses phasic or tonic.
\end{parts} \end{parts}
\end{questions} \end{questions}

3
projects/project_pca_natural_images/pca_natural_images.tex
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@ -27,6 +27,9 @@ In you zip file you find a natural image called {\tt natimg.jpg}.
\question What could be the biological significance of that (\cite{BG} can \question What could be the biological significance of that (\cite{BG} can
give you a clue)? give you a clue)?
\question How could you transform the picture to match the true
representation in the retina (S-, M-, L- cones)?
\end{questions} \end{questions}
\begin{thebibliography}{1} \begin{thebibliography}{1}