Mack Lab News on Mack Lab @ UofT

New paper in JNeuro!

Fri, 10 Jul 2026 00:00:00 +0000

In a new JNeuro paper by Yongzhen (Dory) Xie (which was selected a featured article!), we characterize how hippocampal subfields flexibly update category knowledge representations in the face of novel exceptions. By examining participants’ hippocampal representations before and after exception learning, we captured pattern differentiation and integration in DG, CA2/3, and CA1. In line with existing theories, we show that different subfields exhibit distinct representational shifts in exception learning. Interestingly, these shifts depend on exception type - the learning of a confusable exception (like dolphins that resembles fish but are mammals) involves greater differentiation in DG and integration in CA1, relative to an oddball exception (like the strange-looking platypus)!

Congratulations, Dr. Xie!

Wed, 13 May 2026 00:00:00 +0000

A huge congratulations to Dr. Yongzhen (Dory) Xie! Dory’s victory lap of a final thesis defence was a perfect end to her very successful time in the Mack Lab. Her thesis focused on representational changes that occur during category learning, specifically when learning exceptions to category rules. She incorporated clever empirical tasks, sophisticated computational modelling, and human neuroimaging to comprehensively characterize learning-mediated shifts in how information is organized in conceptual knowledge. Her thesis is an amazing accomplishment and reflects Dory’s hard earned work as a graduate student. We are super proud of Dr. Xie!

New paper on functional footprints published in PNAS!

Fri, 27 Feb 2026 00:00:00 +0000

We are very excited to share Melisa Gumus’ paper, “Distinct contributions of hippocampal pathways in learning regularities and exceptions revealed by functional footprints”, recently published in PNAS. In this work, Melisa proposes a new method that localizes hippocampal pathways with diffusion weighted imaging to interrogate their distinct functional signatures during category learning. She finds that whereas category regularities engage the monosynaptic pathway (i.e., the direct pathway between entorhinal cortex and hippocampal subfield CA1) early in learning, category exceptions engage the trisynaptic pathway (i.e., the pathway that loops in dentate gyrus and CA3) later in learning. These findings provide unique supporting evidence for the functional distinction for these pathways and offer a multimodal approach to further characterizing information flow in the brain. Fun fact: Melisa collected this dataset as an undergrad in 2018!

Congratulations, Dr. Gumus!

Wed, 20 Aug 2025 00:00:00 +0000

A huge congratulations to Dr. Melisa Gumus for successfully defending her PhD thesis! Melisa’s impressive dissertation hit all the corners of the lab’s research: characterizing white matter pathways in the hippocampus and their relationship to cognition, linking computational mechanisms of learning to hippocampal processes and representations, and exploring how attention learning is encoded into flexible concept knowledge. Well done, Dr. Gumus!

Melisa was one of the first trainees in the Mack Lab, starting way back in 2016 as an undergraduate research assistant. In the following 9 years, she wore many hats in the lab including RA, lab manager, graduate RA while she completed a master’s degree with Carmela Tartaglia, and finally PhD student in Psychology. The Mack Lab is what it is today because of Melisa’s persistent motivation for innovative research, her infectious positive spirit, and her gracious support of everyone around her. We will miss her dearly!

Congratulations, Dr. Perovic!

Mon, 21 Jul 2025 00:00:00 +0000

Congratulations to Dr. Mateja Perovic on a very successful defence of her PhD dissertation! Mateja’s dissertation details her impressive and ambitious research on how sex hormones and menstrual cycle impact the core mechanisms of category learning. Spanning behavioural experiments, fMRI, hormone analysis, and genotype testing, Mateja’s PhD work is comprehensive and provides key theoretical insights in fields of cognitive psychology, neuroscience, and women’s health. So very proud of Dr. Perovic!

MackLab at CNS 2025!

Sun, 30 Mar 2025 00:00:00 +0000

Melisa, Mateja, Dory, Sanjivan, and Sagana presented posters on their new findings at Poster Session C and F, on Sunday April 30th and Monday the 31st, respectively.

Poster C21 - Children’s but not adults’ CA2,3/DG differentiates same category information in memory Sagana Vijayarajah, Margaret Schlichting

Poster C49 - Emergence of Attentional Templates in Concept Learning and the Underlying Neural Mechanisms Melisa Gumus, Wen Jia Zhao , Zoey Zhi Yi Lee, Michael L. Mack

Mack Lab at SfN 2024!

Thu, 03 Oct 2024 00:00:00 +0000

We are excited to be presenting new studies and cool findings! Check out Mateja’s poster on Tuesday and Melisa’s talk on Wednesday! Melisa will also be presenting a poster as part of her SfN trainee professional development award! Congratulations!

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/sfn2024_poster_melisagumus.pdf

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/sfn_2024_bdnf.pdf

Talk Category learning builds behaviourally relevant attentional templates Melisa Gumus, Zoey Lee, Michael Mack Wednesday, 8:00-11:15am on October 9th Nanosymposium Human LTM: Encoding and Retrieval III, Room S103

Poster Category learning builds behaviourally relevant attentional templates Melisa Gumus, Zoey Lee, Michael Mack Saturday, 6:30-8:30pm on October 5th Early Career Poster Session, poster board J20 in Hall A

Congratulations, Dr. Heffernan!

Mon, 08 Jul 2024 00:00:00 +0000

Congrats to Dr. Emily Heffernan for successfully defending her PhD thesis! Emily’s PhD studies have provided valuable insights into the attentional and neural mechanisms underlying the learning of surprising categorical information. Emily is now a postdoctoral fellow in the APPLY lab at the University of Toronto Mississauga, where she is investigating digital readability. We are all very proud of you, Dr. Heffernan!

Congratulations, Dr. Son!

Wed, 05 Jun 2024 00:00:00 +0000

Dr. Gaeun Son successfully defended her PhD thesis! Gaeun’s thesis included all her amazing work linking latent spaces of generative AI models to human perception. It is a true accomplishment! Gaeun’s next move is a postdoctoral position in Soojin Park’s lab at Yonsei University. Gaeun will be dearly missed, but we are so excited for her! Congratulations, Dr. Son!

Melisa's data blitz at CEMS 2024

Fri, 31 May 2024 00:00:00 +0000

Melisa gave an excellent data blitz (and was an outstanding Mack Lab representative) at this year’s CEMS. She presented her work on the functional footprints of hippocampal pathways in category learning. Well done, Melisa!

Mack Lab at VSS 2024!

Fri, 17 May 2024 00:00:00 +0000

Mack Lab poster presentations at VSS this year!

Saturday, May 18, 2024, 8:30 am – 12:30 pm

Investigating the representational transformations underlying the learning of exceptions in visual categories
Dory Xie, Emily Q. Wang, Yao Chen, Michael L. Mack

Saturday, May 18, 2024,2:45 – 6:45 pm

Mapping neural similarity spaces for scenes with generative adversarial networks
Gaeun Son, Dirk B. Walther, Michael L. Mack

Sunday, May 19, 2024,2:45 – 6:45 pm

New paper on differentiation and category learning!

Mon, 22 Apr 2024 00:00:00 +0000

Dory Xie published her first paper in Psychonomic Bulletin & Review. In this work, Dory used novel computational modelling & behavioural approaches to show how selective pattern differentiation and integration support learning and generalization of category exceptions. One interesting wrinkle in the data is that latent representational spaces of category items based on a computational model (thanks again, SUSTAIN!) differ from participants’ similarity ratings. Indeed, whereas the model’s latent space shows that category exceptions are differentiated from items that follow category regularities, explicit similarity ratings suggest participants are simply grouping exceptions with their respective category. Maybe similarity ratings don’t reveal cognition’s latent spaces?

Mack Lab at CNS 2024

Thu, 28 Mar 2024 00:00:00 +0000

The Mack Lab will be all over CNS this year!

Saturday

Data blitz session 2, 1-2:30pm ** **Talks by Emily Heffernan and Gaeun Son

Sunday

Poster session B, 8-10am
B151: “Cross-participant neural alignment of attentional states during encoding is linked to better memory in adults and children” Sagana Vijayarajah, Margaret Schlichting
B153: “Menstrual cycle and perceived stress predict performance on the mnemonic similarity” Mateja Perovic, Michael Mack
Poster session C, 5-7pm

New paper on rapid learning of scene wheels!

Mon, 11 Mar 2024 00:00:00 +0000

A new paper from Gaeun Son demonstrates how brief category learning of her novel scene wheel stimuli induces category-specific shifts in people’s scene representations. Gaeun had participants first learn to separate scene stimuli from a scene wheel (defined within the latent space of a generative adversarial network, see Gaeun’s earlier paper for more details) into two categories. After category learning, participants were briefly shown the scenes and had to reconstruct them from working memory. Reconstruction errors showed biases away from the category boundary suggesting the category learning warped the representational scene space. Notably, participants who didn’t learn showed no such biases. And, Gaeun replicated the effects in a second study!

New paper on exception learning and the menstrual cycle!

Thu, 11 Jan 2024 00:00:00 +0000

We are very excited to have Mateja Perovic and Emily Heffernan’s work on exception learning across the menstrual cycle published in Scientific Reports! We found that in a rule-plus-exception category learning task, exception learning performance distinctly varied across the menstrual cycle in a manner consistent with the typical rise and fall of estrogen hormones.

Also, thanks to co-author Gillian Einstein for a great collaboration!

Read the paper here: https://rdcu.be/dtlDi

Mack Lab at SfN 2023

Tue, 07 Nov 2023 00:00:00 +0000

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/sfn2023_poster_melisagumus_edited.pdf

Learning regularities and exceptions are supported by distinct hippocampal pathways as revealed by diffusion-weighted functional footprints Wed., Nov 15, 8am-12pm, Poster SS25 Melisa Gumus is presenting a poster at SfN on an exploratory method we call pathway footprints! Can you use white matter pathways to constrain where to look for behaviourally relevant functional activation? If you’re looking in the hippocampus, the answer seems to be yes! To learn more, see Melisa at SS25 on Nov. 15!

Melisa Gumus awarded NSERC Vanier CGS!

Mon, 28 Nov 2022 00:00:00 +0000

Melisa Gumus was awarded a 2022 NSERC Vanier Canada Graduate Scholarship! This scholarship is only of the most selective and prestigious awards for Canadian graduate students. As described on the Vanier program website: “Vanier Scholars demonstrate leadership skills and a high standard of scholarly achievement in graduate studies in the social sciences and humanities, natural sciences and/or engineering and health”. Congratulations, Melisa!

Mack Lab at SfN 2022!

Tue, 01 Nov 2022 00:00:00 +0000

We are super excited to be back at SfN! Check out Mateja and Emily’s poster on Saturday, Dory’s poster on Sunday, and Melisa Gumus’ talk on Monday:

Talk Distinct hippocampal contributions to the rapid learning of category exceptions Melisa Gumus, Michael Mack Monday, 1:30-1:45pm, Nanosymposium Human LTM: Encoding and Retrieval

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/sfnposter2022_mp_1.pdf

Poster Hippocampus-related exception categorization varies across the menstrual cycle Mateja Perovic, Emily Heffernan, Gillian Einstein, Michael Mack Saturday, 1-5pm, Poster board UU2

Mack Lab at CogSci 2022

Thu, 28 Jul 2022 00:00:00 +0000

We are in-person at CogSci 2022!

Talk: T11.2 - Concepts, Yongzhen (Dory) Xie, Differentiating Exceptions in Rule-Plus-Exception Category Learning| proceedings
**Talk:**T12.2 - Memory and Learning, Bryan Hong, Emphasizing associations from encoding affects free recall at retrieval | proceedings
Poster: Session 6, P6-22-1237, Melisa Gumus, Hippocampus Engagement Early in Learning Supports Concept Formation | proceedings
**Poster:**Session 7, P7-29-1296, Mateja Perović, Category learning across the menstrual cycle: Learning exceptions to the rule varies by hormonal milieu| proceedings
Poster: Session 7, P7-30-2054, Emily Heffernan, An In Silico Exploration of the Effect of Surprising Information on Hippocampal Representations|proceedings

Mateja Perović's poster at CNS 2022!

Thu, 14 Apr 2022 00:00:00 +0000

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/cnsposter2022.pdf

Mateja Perović, a graduate student in Gillian Einstein’s lab, is presenting her outside project in the Mack Lab investigating the role of estrogen on rule-plus-exception learning at CNS 2022. She finds that successfully learning exceptions to category rules varies with the menstrual cycle in a manner that matches the typical time course of estrogen levels across the cycle. These findings are consistent with the known impacts of estrogen on hippocampal function and structure and reveal a key behavioural signature of this cycle-dependent neural variability. Well done, Mateja! Download poster pdf

Melisa Gumus' work on post-concussion syndrome highlighted!

Fri, 25 Mar 2022 00:00:00 +0000

Melisa Gumus’ work on characterizing brain network changes with post-concussion syndrome (PCS) is a featured news item at University Health Network: https://www.uhnresearch.ca/news/after-concussion. Congrats, Melisa!

New paper from Jason Chow's undergraduate research!

Wed, 23 Feb 2022 00:00:00 +0000

Very excited for Jason Chow’s undergraduate research on rapid object categorization published in AP&P! In this paper, Jason looked at the temporal dynamics of object categorization with a novel application of object substitution masking finding an interesting trade-off between basic- and superordinate-level categorization: although superordinate-level categorization demonstrates a clear masking effect very early, it recovers at the first mask offset that impairs basic-level categorization. We argue that this may be evidence of a competitive dynamic between levels of abstraction (e.g., animal vs. dog) during rapid categorization. Jason was one of the first members in the Mack Lab, so excited and proud to have his undergraduate research published! He is currently a graduate student at Vanderbilt University working with Isabel Gauthier and Tom Palmeri.

New paper on exception learning in humans and models!

Thu, 04 Nov 2021 00:00:00 +0000

Very excited for Emily Heffernan’s work on category exception learning to be published in*Scientific Reports.*In this paper, Emily asked if learning exceptions in a rule-plus-exception category learning task can be significantly improved with a learning sequence that promotes hippocampal encoding. The short answer: yes, in both participants and a neural network model of the hippocampus. https://www.nature.com/articles/s41598-021-00864-9

New paper on hippocampal circuitry and category learning

Mon, 16 Aug 2021 00:00:00 +0000

We are excited to publish a new paper in Hippocampus on the relationship between hippocampal circuitry and category learning. We find that the density of white matter connections between hippocampal subfields CA3 and CA1 relate to individual differences in category exception learning. This work comes from our first MRI study conducted at the U of T Psychology Department’s Toronto Neuroimaging Facility. Data collection and analysis efforts were led by incoming graduate student Melisa Gumus and undergraduate student Teresa Zhu and the project was conducted in collaboration with Meg Schlichting.

New paper by Gauen Son for her novel scene wheel method!

Wed, 21 Jul 2021 00:00:00 +0000

Gauen Son’s paper, titled “Scene wheels: Measuring perception and memory of real-world scenes with a continuous stimulus space”, is now published online at Behavior Research Methods. In collaboration with Dirk Bernhardt-Walter, Gaeun developed a novel method for generating continuous stimulus spaces of synthetic naturalistic scenes with a generative adversarial network (GAN). To validate the method, we demonstrated that 1) human judgements of perceptual similarity aligned with distance in the continuous space and 2) the precision of working memory representations (as indexed with a continuous report paradigm) varies according to the geometry of the scene spaces. Here are all the links: paper, OSF page including example code, and demo of working memory experiment. And, check out the press release!

Emily Heffernan wins award at CogSci 2021 Meeting

Tue, 22 Jun 2021 00:00:00 +0000

Emily Heffernan was awarded a Computational Modeling Award in Higher Level Cognition for her submission to the 2021 Cognitive Science Society Meeting. Her conference paper explores the role of hippocampal encoding functions in category learning by integrating human behaviour and computational modelling of the hippocampus. Congrats, Emily! Read more: https://cognitivesciencesociety.org/conference-awards/

Melisa Gumus' study on young-onset Alzheimer's featured!

Thu, 20 May 2021 00:00:00 +0000

Melisa’s recent paper on behavioural markers of young-onset Alzheimer’s disease was featured on U of T Faculty of Medicine’s News: https://medicine.utoronto.ca/news/tanz-centre-findings-may-help-detect-young-onset-alzheimers. Well done, Melisa!

New paper on the neural dynamics of category decisions!

Mon, 10 May 2021 00:00:00 +0000

Congrats to starred first authors Emily and Juliana! Our new paper, “Identifying the neural dynamics of category decisions with computational model-based fMRI” is now published at Psychonomic Bulletin & Review! Read it here: rdcu.be/ckd27

New paper on progression of neuropsychiatric symptoms in Alzheimer’s disease.

Tue, 12 Jan 2021 00:00:00 +0000

Melisa Gumus recently published a longitudinal study showing that the prevalence of anxiety and depression is higher in patients with young-onset of Alzheimer’s than those with late-onset, and the difference remains significant over time: https://link.springer.com/article/10.1007%2Fs11357-020-00304-y. Congrats, Melisa!

Future Leaders in Canadian Brain Research grant!

Mon, 09 Nov 2020 00:00:00 +0000

Mike has been awarded a grant from the 2019 Azrieli Future Leaders in Canadian Brain Research program to study the role of hippocampal white matter pathways in human learning. Read more at Brain Canada

https://braincanada.ca/news/major-boost-for-brain-health-in-canada/

8 months of news from the Mack Lab!

Fri, 06 Nov 2020 00:00:00 +0000

A very much overdue recap of many successes and achievements over the past year!

Belinda Hoang, Teresa Zu, Victoria Liu, Zi Cheng, and Dmitri Saharov all graduated!
Zoe Wu was awarded an NSERC USRA fellowship for the summer (which went very well!)
Aaron Rambhajan finished his U of T Master of Information degree!
Melisa Gumus successfully defended her MSc thesis in the Uof T Institute for Medical Sciences!
Juliana Adema and Emily Heffernan were award NSERC CGS-M fellowships!
Juliana Adema and Emily Heffernan also successfully defended the Masters theses!
We were also awarded a New Frontiers in Research Fund Transformation grant for our work on the impact of indoor air quality on cognition!

New paper! vmPFC compression during category learning

Tue, 07 Jan 2020 00:00:00 +0000

Very excited about our new paper: “Ventromedial prefrontal cortex compression during learning”. vmPFC coding akin to goal-directed dimensionality reduction and tracks attention weights from learning models. https://www.nature.com/articles/s41467-019-13930-8

New paper on the brain mechanisms for concept learning

Sun, 20 Oct 2019 00:00:00 +0000

Excited for our new paper published in Journal of Neuroscience! This paper is a companion review for the SfN 2019 minisymposium co-chaired by Dasa Zeithamova and Michael Mack. https://www.jneurosci.org/content/39/42/8259

SfN 2019 posters from the MackLab

Sun, 20 Oct 2019 00:00:00 +0000

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/gumus_etal_sfn2019.pdf

Hippocampal white matter microstructure predicts rapid category learning Melisa Gumus, Teresa Zhu, Meg Schlichting, and Michael Mack

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/cheng_etal_sfn2019.pdf

Early hippocampal engagement supports flexible category learning Ziming Cheng, Tong Liu, and Michael Mack

Welcome to our new graduate students!

Sat, 21 Sep 2019 00:00:00 +0000

Very excited to welcome Juliana Adema, Emily Heffernan, and Gaeun Son to the lab as new graduate students!

New paper on hippocampal subfield segmentation

Mon, 06 May 2019 00:00:00 +0000

Excited to have our new paper published: "Comparison of semi-automated hippocampal subfield segmentation methods in a pediatric sample"

New grant on the neurocognitive impacts of indoor air quality

Tue, 16 Oct 2018 00:00:00 +0000

We’re excited to start work on a new collaborative project on the neurocognitive impact of indoor air quality. This project is in collaboration with Jeffrey Siegel in the U of T Department of Civil and Mineral Engineering and is funded by an XSeed Grant from the U of T Faculties of Arts & Science and Engineering.

Graduation Excitement at Macklab; Well Done, Marlie, Jason and Melisa!

Wed, 20 Jun 2018 00:00:00 +0000

Congrats to Marlie, Jason and Melisa on completing their bachelor’s degree with success. Macklab was happy to share the excitement of their graduation day, and thank you to Teresa, Chanel and Belinda for surprising us with creative and fun posters!

Congrats to Marlie, UTEA for Summer 2018!

Tue, 01 May 2018 00:00:00 +0000

Congrats to Marlie for receiving an University of Toronto Excellence Award (UTEA) for Summer 2018!

Congrats to Teresa, USRA for Summer 2018!

Sun, 01 Apr 2018 00:00:00 +0000

Congrats to Teresa for receiving an NSERC Undergraduate Student Research Award (USRA) for Summer 2018!

Marlie Presents at the Undergraduate Psychology Thesis Poster Conference

Thu, 29 Mar 2018 00:00:00 +0000

Marlie presented her undergraduate thesis as part of her undergraduate specialist program! Well-done!

Congrats to Jason, again! OPAM best poster award!

Tue, 21 Nov 2017 00:00:00 +0000

Congratulations to Jason Chow, again! Jason received an award for best poster at OPAM. Well done!

MackLab research at OPAM/Psychonomics/SfN 2017

Tue, 07 Nov 2017 00:00:00 +0000

Medial prefrontal cortex compresses concept representations through learning Authors: Michael Mack (contact), Alison Preston, and Brad Love

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/macklovepreston_2017.pdf

Object substitution masking reveals a competitive dynamic between levels of categorization Authors: Jason Chow (contact) and Michael Mack

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/chow_mack_opam2017.pdf

Congrats to Jason, OPAM travel award!

Fri, 15 Sep 2017 00:00:00 +0000

Congratulations to Jason Chow for being awarded an OPAM Student Travel Award! Jason will be presenting a poster at OPAM 2018 on his recent work looking at the time course of categorization with object substitution masking:

Chow, J.K., & Mack, M.L. (2017). Object substitution masking reveals a competitive dynamic between levels of categorization. Poster presentation at the Object Perception, Attention, and Memory Annual Conference 2018, Vancouver, B.C.