Vision Lunch 2009

From VISTA LAB WIKI

Jump to: navigation, search

Return to Vision Lunch current schedule

Contents

[edit] 2009 Vision Lunches

[edit] January

7 Noa Ofen

Developmental Changes in the Encoding of Indoor versus Outdoor scenes

Regions in the medial temporal lobe (MTL) including the parahippocampal cortex (PHC) are involved in memory formation. Previously we showed that activations in MTL for successful memory encoding of indoor and outdoor scenes does not change with age (Ofen et al., 2007). Indoor and outdoor scenes, however, differ in their statistical properties and complexity. Moreover, in adults, viewing of indoor scenes is associated with greater activation in the posterior PHC when compared to viewing outdoor scenes (Henderson et al., 2007). The development of brain activation for processing of indoor versus outdoor scenes is unknown although; there is evidence of developmental changes in brain regions involved in the processing of scenes (Golarai et al., 2007). Furthermore, the potential contribution of these activations to memory formation is unclear. In this talk I will present data regarding the development of brain regions for processing of indoor and outdoor scenes in the context of subsequent memory formation in 49 participants (ages 8 - 24). We found that memory for indoor, but not outdoor, scenes increased with age. Overall, indoor scenes compared to outdoor scenes activated bilateral posterior PHC and retrospelenial cortex and, within these regions, the activation in the right posterior PHC increased with age. Using a complexity index we further found that recollection for indoor scenes with high complexity increased with age and the activation in the right posterior hippocampus increased with age for more complex indoor scenes. Collectively, these findings suggest prolonged developmental trajectory of posterior MTL regions and their roles in successful memory recollection.


14 Daniel Palanker Electronic Retinal Prostheses for Restoration of Sight to the Blind

Electronic retinal prostheses aim to restore sight in patients with retinal degeneration by patterned electrical stimulation of surviving inner retinal neurons. Design of a high-resolution prosthesis presents many engineering and biological challenges. Large number of stimulating electrodes should be placed close to the target retinal neurons to prevent blurring and minimize current. Signals must be delivered wirelessly to thousands of electrodes, and visual information should, ideally, maintain its natural link to eye movements. Finally, a good system must have a wide range of stimulation currents and external control of image processing. I will review the current status of the field, including results of human implantations, and describe the achievements and challenges in this path. I will also present the Optoelectronic Retinal Prosthesis currently developed and tested at Stanford.

21 Moriah Thomason

Reconsidering perfusion at the baseline of BOLD: a COMT gene story

Levels of extra-synaptic dopamine in the brain vary in part as a function of polymorphisms on the catechol-O-methyltransferase (COMT) gene. In vivo studies of the effects of COMT in the human brain have typically measured patterns of neural activation during dopamine-mediated tasks in adults. The present study is the first to investigate the effects of COMT both on the brain during rest and on brain physiology in children. We used flow-sensitive arterial spin labeling (ASL) magnetic resonance imaging to examine brain blood flow (bBF) in 42 children. Met-allele homozygotes exhibited greater bBF in mesolimbic, mesocortical, and nigrostriatal dopamine (DA) pathways. Higher perfusion in DA-rich brain structures reflects COMT-related baseline differences that (1) underlie the selective behavioral advantages associated with each genotype; (2) affect interpretations of previously reported genotype differences in BOLD signal changes; and (3) serve as a foundation for future studies of the effects of COMT genotype on brain development.

28 Voodoo Correlations in Social Neuroscience

[edit] February

4 Neural Basis of BOLD

  • Neurometabolic coupling in cerebral cortex reflects synaptic more than spiking activity
Ahalya Viswanathan & Ralph D Freeman
Nature Neuroscience 10, 1308 - 1312 (2007)
http://www.nature.com/neuro/journal/v10/n10/abs/nn1977.html
  • BOLD and spiking activity
Yuval Nir, Ilan Dinstein, Rafael Malach & David J Heeger
Nature Neuroscience 11, 523 - 524 (2008)
http://www.nature.com/neuro/journal/v11/n5/full/nn0508-523.html
  • Reply to "BOLD and spiking activity"
Ahalya Viswanathan & Ralph D Freeman
Nature Neuroscience 11, 524 (2008)
http://www.nature.com/neuro/journal/v11/n5/full/nn0508-524.html

11 Plasticity

  • Changes in connectivity after visual cortical brain damage underlie altered visual function
Holly Bridge, Owen Thomas, Saâd Jbabdi and Alan Cowey
http://brain.oxfordjournals.org/cgi/content/full/131/6/1433
  • see also comment:
The anatomy of blindsight.
Rees G.
http://brain.oxfordjournals.org/cgi/content/full/131/6/1414


18 No Vision Lunch

25 Discussion: Feedback of visual object information to foveal retinotopic cortex Williams MA, Baker CI, Op de Beeck HP, Shim WM, Dang S, Triantafyllou C, Kanwisher N. Nat Neurosci. 2008 Dec;11(12):1439-45. Epub 2008 Nov 2

http://tinyurl.com/dxexur

The mammalian visual system contains an extensive web of feedback connections projecting from higher cortical areas to lower areas, including primary visual cortex. Although multiple theories have been proposed, the role of these connections in perceptual processing is not understood. We found that the pattern of functional magnetic resonance imaging response in human foveal retinotopic cortex contained information about objects presented in the periphery, far away from the fovea, which has not been predicted by prior theories of feedback. This information was position invariant, correlated with perceptual discrimination accuracy and was found only in foveal, but not peripheral, retinotopic cortex. Our data cannot be explained by differential eye movements, activation from the fixation cross, or spillover activation from peripheral retinotopic cortex or from lateral occipital complex. Instead, our findings indicate that position-invariant object information from higher cortical areas is fed back to foveal retinotopic cortex, enhancing task performance.

[edit] March 2009

4 Discussion: How silent is the brain: is there a "dark matter" problem in neuroscience?

(suggested by Nikos Logothetis)

Shoham S, O'Connor DH, Segev R J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2006 Aug;192(8):777-84

http://www.ncbi.nlm.nih.gov/pubmed/16550391

18 Talk: Daniel Baldauf, Visual preparation of multiple movement goals
Ludwig-Maximilians-University, Munich, Germany
Many actions that we perform everyday are complex, coordinated concatenations of single movements. In a first series of experiments, we studied how visual attention guides the selection of several subsequent goal positions of intended eye- or hand- movement sequences. We used a secondary letter discrimination task and ERP analyses to probe how visual attention was distributed during the short movement preparation period after the go-signal, but well before onset of the first movement.

The results showed that during movement preparation attention split into multiple spatially distinct foci and selected in parallel all intended movement goals. The movement preparation caused facilitated visual processing of the target locations in early visual areas. Further, the behavioural data suggest that there is a gradient of the attentional weights assigned to the individual goals, with more visual resources being deployed to the first goal of the sequence and less to the second and third.

A second series of experiments used single-cell recordings in the parietal cortices of two behaving monkeys. The data suggest that the posterior parietal cortex (PPC) encodes in parallel multiple goals for a planned hand movement sequence. We argue that the planning activity in PPC provides a likely source of top-down attentional signals that selectively enhance visual perception at all intended positions of a motor sequence.

25 Talk: Stephen Frost, Neuroimaging studies of reading development and reading disability
Haskins Lab, Yale University. (Hosted by Bob Dougherty.)

[edit] April 2009

1 No Vision Lunch

8 Alex Wade: "The negative BOLD effect and its behavioral correlates"


15 Discussion: Treating congential blindness in dogs and humans

Aguirre et al, PLoS Medicine 2007

RPE65 is an essential molecule in the retinoid-visual cycle, and RPE65 gene mutations cause the congenital human blindness known as Leber congenital amaurosis (LCA). Somatic gene therapy delivered to the retina of blind dogs with an RPE65 mutation dramatically restores retinal physiology and has sparked international interest in human treatment trials for this incurable disease. An unanswered question is how the visual cortex responds after prolonged sensory deprivation from retinal dysfunction. We therefore studied the cortex of RPE65-mutant dogs before and after retinal gene therapy. Then, we inquired whether there is visual pathway integrity and responsivity in adult humans with LCA due to RPE65 mutations (RPE65-LCA).


22 Mark Churchland, Stanford University
Stimulus onset quenches neural variability: a widespread cortical phenomenon


29 Discussion: Working memory in primary visual cortex

http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature07832.html

http://www3.interscience.wiley.com/journal/121633777/abstract

[edit] May 2009

6 VSS preparation

13 VSS: No Vision Lunch

20 VSS rehash

27 No Vision Lunch

[edit] June

3 Alex Huk (Neurobiology & Center for Perceptual Systems, The University of Texas at Austin)

Neural basis of 3D motion perception

Although much is known about how the primate visual system encodes both 2D motion and static depth, relatively little is known about how retinal motions and changing binocular disparities are used to perceive 3D motion. A fundamental question is whether the visual system encodes 3D direction by estimating changes in binocular disparity over time, or by computing interocular differences in patterns of retinal motion. In this talk I'll describe a series of human psychophysical and physiological experiments investigating the processing of these two primary binocular cues to 3D motion direction. A series of initial psychophysical experiments demonstrate that the visual system relies upon both differences in retinal velocities and changes in disparity over time, although these two cues exhibit vastly different speed tuning. A series of brain imaging experiments demonstrate that both of these cues are represented in human visual area MT+, but not in earlier cortical regions. A final set of psychophysical experiments suggest that the computation of interocular velocity differences operates upon eye-specific pattern motion signals. Taken together, these results demonstrate that the study of 3D motion is tractable, and stands to reveal novel signals in both well-understood and as-of-yet-unidentified brain circuits.

10 HBM practice

[edit] July

8 Receptive fields in human visual cortex mapped with surface electrodes. (Andreas and Janice)
Yoshor D, Bosking WH, Ghose GM, Maunsell JH.

Most of our understanding of the functional organization of human visual cortex comes from lesion and functional imaging studies and by extrapolation from results obtained by neuroanatomical and neurophysiological studies in nonhuman primates. Although some single-unit and field potential recordings have been made in human visual cortex, none has provided quantitative characterization of spatial receptive fields (RFs) of individual sites. Here we use subdural electrodes implanted for clinical purposes to quantitatively measure response properties in different regions of human visual cortex. We find significant differences in RF size, response latency, and response magnitude for sites in early visual areas, versus sites in later stages of both the dorsal and ventral streams. In addition, we use this technique to estimate the cortical magnification factor in early human visual cortex. The spatial and temporal resolution of cortical surface recordings suggest that this technique is well suited to examine further issues in visual processing in humans.

15 Dana Kuefner: visitor from Rossion's lab at Université catholique de Louvain

Behavioral studies indicate that our ability to process faces develops until about 16 years of age. However, whether this development is specific to our ability to process faces or a product of general age-related improvements in many other cognitive factors (attention, planning, memory...) is still unclear.

Here, we tested over 65 children between the ages of 5 and 18, and a group of adults (N=12). We recorded ERPs from 62 scalp electrodes in response to faces and well-controlled visual stimuli, namely phase-scrambled faces. We also added a familiar nonface object category (cars) to control for the effect of shape, and its scrambled counterpart. Subjects’ task was to distinguish between object shapes (faces or cars) and their scrambled versions. When considering raw responses to faces, we replicated previous studies’ observations on the P1 and N170: P1 decreases in amplitude across development, N170 increases and latency decreases, with substantial differences in N170 scalp topographies across age. However, we found none of these observations to be specific to faces, but rather, to be general characterizations of responses to visual stimuli. The occipital P1 was larger in response to faces than cars, but the exact same effect was found for their scrambled counterpart, across all ages, indicating that this early sensitivity to faces is based on low-level cues available to all visual systems between 5 and 18 years old. Its amplitude variation across age was equivalent for each of the stimuli.

The N170 – corresponding to the activation of face representations in the human brain – was isolated from the P1 by peak-to-peak analysis and subtraction waveforms. In doing so, we found that the N170 is present at 5 years of age, and shows the same profile as in adults: larger for faces than cars (and absent for scrambled stimuli), with the exact same topography. Its latency was slightly delayed, but equally so for the other visual stimuli, merely reflecting a general developmental trend. Finally, we found that a “bi-fid” N170 observed in younger years is clearly a merging of the N170 with a later component (the N250) likely due to a larger amount of variance in the data of young children. Nevertheless, the real N170 is easily identifiable in the majority of young children’s data, emphasizing the need to treat subjects as individuals, rather than interpreting data based on grand-averaged waveforms for different age-groups. Our data have significant implications for the use of ERPs with developmental populations. Most importantly, they highlight the need for researchers to adopt an approach of isolating stimulus specific effects in order to make reliable comparisons of ERP data across age groups, without resorting to grand-averaging within different age-groups which do not present the same variability in brain responses.

22 Discussion: The Foveal Confluence in Human Visual Cortex
http://www.jneurosci.org/cgi/content/full/29/28/9050

29 Elena Rykhlevskaia
Structural brain correlates of math ability

Mathematical disabilities are relatively common in children, yet poorly understood. Functional neuroimaging studies have suggested involvement of a network of brain regions involving posterior parietal, inferior temporal and prefrontal cortex as being important for mathematical cognition. We used structural MRI and diffusion tensor imaging (DTI) to investigate whether structural impairments within this network contribute to math disability.

[edit] August

5-12 HIATUS


19 DISCUSSION: A face space in macaque IT face patches

A face feature space in the macaque temporal lobe

Winrich A Freiwald, Doris Y Tsao & Margaret S Livingstone

The ability of primates to effortlessly recognize faces has been attributed to the existence of specialized face areas. One such area, the macaque middle face patch, consists almost entirely of cells that are selective for faces, but the principles by which these cells analyze faces are unknown. We found that middle face patch neurons detect and differentiate faces using a strategy that is both part based and holistic. Cells detected distinct constellations of face parts. Furthermore, cells were tuned to the geometry of facial features. Tuning was most often ramp-shaped, with a one-to-one mapping of feature magnitude to firing rate. Tuning amplitude depended on the presence of a whole, upright face and features were interpreted according to their position in a whole, upright face. Thus, cells in the middle face patch encode axes of a face space specialized for whole, upright faces.


26 DISCUSSION: Continuous Carry-Over Adaptation Methods

Distinguishing Conjoint and Independent Neural Tuning for Stimulus Features With fMRI Adaptation

Drucker DM, Kerr WT, Aguirre GK. Distinguishing conjoint and independent neural tuning for stimulus features with fMRI adaptation.

J. Neurophysiol 101: 3310–3324, 2009. First published April 8, 2009; doi:10.1152/jn.91306.2008.

A central focus of cognitive neuroscience is identification of the neural codes that represent stimulus dimensions. One common theme is the study of whether dimensions, such as color and shape, are encoded independently by separate pools of neurons or are represented by neurons conjointly tuned for both properties. We describe an application of functional magnetic resonance imaging (fMRI) adaptation to distinguish between independent and conjoint neural representations of dimensions by examining the neural signal evoked by changes in one versus two stimulus dimensions and considering the metric of two-dimension additivity. We describe how a continuous carry-over paradigm may be used to efficiently estimate this metric. The assumptions of the method are examined as are optimizations. Finally, we demonstrate that the method produces the expected result for fMRI data collected from ventral occipitotemporal cortex while subjects viewed sets of shapes predicted to be represented by conjoint or independent neural tuning.

The above paper is mostly about the theory of the approach We will also discuss the following related paper, which uses the approach in a particular example (time permitting):

Drucker and Aguirre, Cerebral Cortex 2009: Different Spatial Scales of Shape Similarity Representation in Lateral and Ventral LOC.


[edit] September

3 (Note: rescheduled to Thursday at 12 pm)
Discussion: Category-Specific Organization in the Human Brain Does Not Require Visual Experience Pages 397-405
Bradford Z. Mahon, Stefano Anzellotti, Jens Schwarzbach, Massimiliano Zampini, Alfonso Caramazza
doi:10.1016/j.neuron.2009.07.012
http://www.cell.com/neuron/abstract/S0896-6273%2809%2900541-8

9 Discussion: Contrast sensitivity, adaptation, and natural scenes.

Contrast sensitivity in natural scenes depends on edge as well as spatial frequency structure
Peter J. Bex, Samuel G. Solomon, Steven C. Dakin http://journalofvision.org/9/10/1/


16 Discussion: Retinotopic Organization of Human Ventral Visual Cortex

Michael J. Arcaro,1,2 * Stephanie A. McMains,1,2 * Benjamin D. Singer,2 and Sabine Kastner1,2,3

http://www.jneurosci.org/cgi/content/full/29/34/10638

Functional magnetic resonance imaging studies have shown that human ventral visual cortex anterior to human visual area V4 contains two visual field maps, VO-1 and VO-2, that together form the ventral occipital (VO) cluster (Brewer et al., 2005Go). This cluster is characterized by common functional response properties and responds preferentially to color and object stimuli. Here, we confirm the topographic and functional characteristics of the VO cluster and describe two new visual field maps that are located anterior to VO-2 extending across the collateral sulcus into the posterior parahippocampal cortex (PHC). We refer to these visual field maps as parahippocampal areas PHC-1 and PHC-2. Each PHC map contains a topographic representation of contralateral visual space. The polar angle representation in PHC-1 extends from regions near the lower vertical meridian (that is the shared border with VO-2) to those close to the upper vertical meridian (that is the shared border with PHC-2). The polar angle representation in PHC-2 is a mirror reversal of the PHC-1 representation. PHC-1 and PHC-2 share a foveal representation and show a strong bias toward representations of peripheral eccentricities. Both the foveal and peripheral representations of PHC-1 and PHC-2 respond more strongly to scenes than to objects or faces, with greater scene preference in PHC-2 than PHC-1. Importantly, both areas heavily overlap with the functionally defined parahippocampal place area. Our results suggest that ventral visual cortex can be subdivided on the basis of topographic criteria into a greater number of discrete maps than previously thought.


23 Talk - Dr. Andy Huberman: Genetic dissection of visual circuits (Barres lab postdoc, DY hosting)

What are the neural circuits underlying vision? Retinal ganglion cells (RGCs) are the output neurons of the eye and thereby the source of all visual information for the brain. Over a century of study has established there are ~20 different RGC subtypes, each encoding a qualitatively distinct aspect of the visual scene such as luminance, color, dark edges, etc. Where each RGC subtype sends that information in the brain and how the outputs of different RGC subtypes are integrated with each other to influence visual processing, remains unclear. I use mouse genetic techniques to identify and visualize functionally distinct RGC subtypes and to map their central projections. This approach has revealed a remarkable degree of wiring specificity for RGC subtypes encoding distinct aspects of motion, direction and luminance. These findings support the idea of multiple visual ‘sub-systems’, each pooling inputs from different combinations of RGC subtypes and thereby mediating specific aspects of visual perception and behavior. Genetic analyses are beginning to reveal the logic of how functionally distinct visual circuits are specified and assembled during development and are providing clues about the molecular pathways that may designate specific visual processing streams in primates.


[edit] October

7 Cancelled

14 SFN prep

21 SFN - No Vision Lunch??

28 DISCUSSION: Resting GABA concentration predicts peak gamma frequency and fMRI amplitude in response to visual stimulation in humans.
Muthukumaraswamy et al, PNAS.

http://www.pnas.org/content/106/20/8356.full

Functional imaging of the human brain is an increasingly important technique for clinical and cognitive neuroscience research, with functional MRI (fMRI) of the blood oxygen level-dependent (BOLD) response and electroencephalography or magnetoencephalography (MEG) recordings of neural oscillations being 2 of the most popular approaches. However, the neural and physiological mechanisms that generate these responses are only partially understood and sources of interparticipant variability in these measures are rarely investigated. Here, we test the hypothesis that the properties of these neuroimaging metrics are related to individual levels of cortical inhibition by combining magnetic resonance spectroscopy to quantify resting GABA concentration in the visual cortex, MEG to measure stimulus-induced visual gamma oscillations and fMRI to measure the BOLD response to a simple visual grating stimulus. Our results demonstrate that across individuals gamma oscillation frequency is positively correlated with resting GABA concentration in visual cortex (R = 0.68; P < 0.02), BOLD magnitude is inversely correlated with resting GABA (R = −0.64; P < 0.05) and that gamma oscillation frequency is strongly inversely correlated with the magnitude of the BOLD response (R = −0.88; P < 0.001). Our results are therefore supportive of recent theories suggesting that these functional neuroimaging metrics are dependent on the excitation/inhibition balance in an individual's cortex and have important implications for the interpretation of functional imaging results, particularly when making between-group comparisons in clinical research

[edit] Nov

4 Roozbeh Kiani will talk about his research on perceptual decisions

11 Discussion with Shimon Ullman
Prof. Ullman has suggested reading the 2008 paper below, which builds on an earlier 2002 result (also below)


Proc Natl Acad Sci U S A. 2008 Sep 23;105(38):14298-303. Epub 2008 Sep 16.
Image interpretation by a single bottom-up top-down cycle.
Epshtein B, Lifshitz I, Ullman S.
Department of Computer Science, The Weizmann Institute of Science, Rehovot 76100, Israel.
The human visual system recognizes objects and their constituent parts rapidly and with high accuracy. Standard models of recognition by the visual cortex use feed-forward processing, in which an object's parts are detected before the complete object. However, parts are often ambiguous on their own and require the prior detection and localization of the entire object. We show how a cortical-like hierarchy obtains recognition and localization of objects and parts at multiple levels nearly simultaneously by a single feed-forward sweep from low to high levels of the hierarchy, followed by a feedback sweep from high- to low-level areas.


Nat Neurosci. 2002 Jul;5(7):682-7.
Visual features of intermediate complexity and their use in classification.
Ullman S, Vidal-Naquet M, Sali E.
Department of Computer Science and Applied Mathematics, The Weizmann Institute of Science, PO Box 26, Rehovot 76100, Israel. shimon.ullman@weizmann.ac.il
The human visual system analyzes shapes and objects in a series of stages in which stimulus features of increasing complexity are extracted and analyzed. The first stages use simple local features, and the image is subsequently represented in terms of larger and more complex features. These include features of intermediate complexity and partial object views. The nature and use of these higher-order representations remains an open question in the study of visual processing by the primate cortex. Here we show that intermediate complexity (IC) features are optimal for the basic visual task of classification. Moderately complex features are more informative for classification than very simple or very complex ones, and so they emerge naturally by the simple coding principle of information maximization with respect to a class of images. Our findings suggest a specific role for IC features in visual processing and a principle for their extraction.

18 Daniel Adams, UCSF: Perceptual suppression in strabismus

25 Thanksgiving - No Vision Lunch

[edit] Dec

9 David Ress will visit and tell us what they are up to at UT Austin

16 OPEN

23 Christmas

30 New Year's

Personal tools