[Comp-neuro] [PhD] Natural scene statistics and visual motion processing in humans and non-human primates
laurent.perrinet at univ-amu.fr
Tue Jun 3 10:40:19 CEST 2014
Applications are invited for 3 PhD positions funded by the PhD program in Integrative and Clinical Neurosciences (http://www.int.univ-amu.fr/PhD-Program-in-Integrative-and), as described in:
among which the following ---at the Institute of Neurosciences, Timone in Marseille, France--- may be of interest to the list.
Deadline for applications is June 15th.
Laurent Perrinet - INT (UMR 7289)/CNRS
Title: Natural scene statistics and visual motion processing in humans and non-human primates
Supervisor: Guillaume MASSON
Laboratory: Institute of Neurosciences, Timone (INT)
State of the art: The mammalian visual system is tuned to process the complex, high-dimension statistics
of natural scenes. For instance, neuronal responses to natural inputs are more ﬁnely tuned, more
temporally precise and more sparse. A major challenge is to understand how such complex information is
integrated to measure perceptual quantities such as object motion in a crowded environment. From a
theoretical perspective, this implies to understand how the cascade of cortical processing steps extracts the
relevant dimensions through linear (e.g. ﬁltering) and nonlinear (e.g. gain control, contextual modulation)
mechanisms. From an experimental perspective, the challenge implies to design behavioural tasks that can
dissect out these mechanisms. The classical approach is to compare classic, low-dimension stimuli such as
gratings or dots with natural images. However, it is almost impossible to parametrize natural scenes in a
useful way. We , and others , have designed and begun to use naturalistic stimuli as static or dynamic
textures of which mean and variance along each parameter space is manipulated to demonstrate how
sensory systems sense and represent information. We have recently shown in Nature Neuroscience3 that
richer textures drive more accurate and reliable ocular tracking responses. This is the ﬁrst demonstration
that naturalistic inputs processing can be probed using sensorimotor tasks.
Objectives: Our objective is to demonstrate that in human and non-human primates, estimating direction
and speed of a moving object requires to integrate information from the multiple spatial and temporal
scales existing in natural scenes. We will investigate how different spatiotemporal frequency channels are
nonlinearly combined to drive faster and more precise tracking eye movements. In particular, we will
extend our previous study  by studying how richness of visual motion information reduces the variability
of motor responses, within and across trials. We will also study how the geometric organization of the
texture input impacts performance, opening the door to understanding the link between low-level motion
processing and the perceptual organization of complex scenes.
Methods: The approach is based on probing low-level visual processing through the dynamics of
reﬂexive eye movements. Ocular following responses exist in both humans and non-human primates and
over the last 15 years we, and others have shown how they can probe low-level motion mechanisms. The
PhD will work in non-human primates to conduct behavioural experiments using random phase textures
and recording eye movements with the scleral search coil technique. Behavioural performance will be
assessed through kinematics (acceleration, latency…) as well as through detection and discrimination
tasks (i.e. comparison between responses for two stimuli).
Expected results: A ﬁrst step will be to reproduce the main observation made in humans: richness of the
inputs improves precision and decreases variability. Then we will characterize the nonlinear interactions
between spatiotemporal channels underlying speed estimation through motion energy and their temporal
Feasibility: This project is supported by an ANR project (SPEED) that started in October 2013. The PhD
student will work in close collaboration with a PD fellow working in humans as we expect the ﬁrst series
of experiments to be identical in both species. A non-human primate set-up is available and a research
assistant (F Barthelemy) will daily supervise the lab work. The InViBe team has strong expertises in
modelling and electrophysiology so that the project will open the door for collaborative work in texture
synthesis and speed processing modelling with Laurent Perrinet and recording of population activity
evoked with dense, naturalistic textures with Fred Chavane.
1 Sanz-Léon et al. (2012) J Neurophysiol http://invibe.net/LaurentPerrinet/Publications/Sanz12
2 Freeman et al. (2013) Nature Neuroscience
3 Simoncini et al. (2012) Nature Neuroscience http://invibe.net/LaurentPerrinet/Publications/Simoncini12
Listed as Research project #18 in:
In 2014, the PhD program in Integrative and Clinical Neurosciences will fund three PhD scholarships to excellent Master graduates from non-French top ranked universities
The selection process includes the following steps :
Nineteen research projects of excellence from AMU laboratories have been selected by the board of the PhD program.
Applicants have to select and rank two research projects and motivate their choice
The selection committee will shortlist 10 students that will be individually interviewed in June
The final decision will be known in July and the three successful candidates will start their PhD in October.
Guidelines for students
The scholarships are open to high performing Master graduates from top ranked non-French universities.
Applicants must provide the following documents :
A first e-mail should be sent by you to edsvs-neuroscience-phd-program at univ-amu.fr with the subject "PhD Application, YourName"  and three documents in the appropriate format :
a Curriculum Vitae. This document should be named "YourName_CV.doc"
a document highlighting the adequacy between the applicant’s background and the selected research projects (to be download here). Please use the following template to be download here. This document should be named "YourName_ResearchProjects.doc" .
a one page letter of motivation (500 words). This document should be named "YourName_motivation_letter.doc" .
two letters of recommendation will have to be sent directly to edsvs-neuroscience-phd-program at univ-amu.fr with the subject "Recommendation, YourName" , using the following template to be download here. This document should be named "YourName_Evaluation.doc".
Closing date for applications : Sunday, June 15th, at midnight (French time).
Scholarship value : Net monthly salary : 1,368 €.
Expenses : applicants will pay their annual tuition fee (around 500 €) and, when needed, their visa fee.
Tenure of award : 3 years
Any incomplete application will not be considered
How and when do students learn about the decision ? Offers of PhD scholarships will be made soon after the final individual interview, early July. Because some applicants may decline a scholarship, it is possible that some applicants receive their notification of selection a week after the final decision
What conditions are attached to acceptance of this award ? Scholarship recipients must sign a Postgraduate Scholarships Contract agreeing to abide by the attached regulations. Recipients will be required to devote themselves full-time to their program of research during the tenure of the scholarship
Selection committee : members of the PhD program board and members of the AMU neuroscience community. None of them will be the supervisor of a proposed research project
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