Gregor M. Hörzer


This is a brief overview over some of the things I typically think and write about.

Metaphysics of Science

Currently, I am mainly working on some metaphysical questions in the philosophy of science. In particular, I address issues regarding the new mechanist framework that aims at mainly capturing explanatory practices in the life sciences, such as cognitive science, neuroscience and biology. My aim is to critically analyze the metaphysical implications of the accounts suggested in the literature and to propose an alternative account that avoids the metaphysical difficulties of its rivals.


Metaphysics of Mind (and beyond)

In the metaphysics of mind and the world more generally, I have investigated the formulation question regarding the thesis of physicalism (roughly: the thesis that there is nothing over and above the physical). I have proposed a formulation that is quite rigorous compared to other formulations in the literature. I have taken care to make my formulation of physicalism compatible with the existence of certain things that physicalists are not really concerned with, such as numbers and haecceitistic properties, and have argued that physicalism is mainly a thesis about how the properties of individuals and relations between individuals relate to physical properties and relations of individuals via metaphysical dependency relations between those properties and relations.

I have argued for a novel account of the notion of a physical property that features in the thesis of physicalism which satisfies a number of intuitively plausible constraints on such notion that other accounts prevalent in the literature fail to satisfy. One central idea that sets apart my account from many of its traditional rivals is that physical properties have to share a common nature: whatever it is that makes them physical. By using a variety of otherwise widely different prototype cases of physical properties, we can then frame physical properties as all and only those properties that share the common nature of the prototypes (along with some further constraints). Interestingly, my account of physical properties makes physicalism compatible with certain forms of panpsychism, as well as with certain forms of idealism, but I argue that this is a feature rather than a bug.

With regard to the metaphysical dependence relation required, I argue that a certain form of supervenience is necessary but not sufficient for metaphysical dependence, and suggest that a more fine-grained dependence relation (not unlike what is known as Grounding) might be a better candidate for the required relation between physical and other properties of individuals. I argue that there is work to do for Grounding, and even if it turns out that a generic Grounding relation is not required, then at least there is work to do for a generic concept of Grounding, as it can help to pick out the various metaphysical dependence relations discussed in the literature, such as different varieties of the realization relation and the determinable-determinate relation.

For a in-depth discussion of these and a wide variety of related issues, please refer to my book Understanding Physicalism.

Other Philosophical Topics

Aside from my main areas of interest, I also occasionally think about issues in the philosophy of language, with a strong focus on Saul Kripke's work and work based on his work, i.e. direct reference theory, two-dimensional semantics and the like. My book Saul Kripke: Identity and Necessity is one outcome of this line of thinking. 

I also sometimes think about views of cognition and consciousness, with a special interest in boundary cases and extravagant positions, such as plant cognition and plant consciousness, which I find to be a highly interesting topic even though I am rather skeptical that a reasonably sophisticated account of cognition (and more so with consciousness) will be applicable to plants. As far as I can tell, most accounts that plausibly capture plants, such as enactivist views of cognition, construe cognition so broadly that plants are not boundary cases, but may rather be considered prototypes of cognitive systems. In this case, the claim of plant cognition turns out to be much less bold than it seems at first glance. 

Furthermore, I am a clear defender of the view that we have to take first-person experience seriously, and think that eliminativist/illusionist views about first-person experience do not satisfy this constraint. In my article Cognitive Naturalism and the Phenomenal Feel, published in the journal Rivista Internazionale di Filosofia e Psicologia, I argue against Sandro Nannini's version of eliminative materialism and his suggestion that we can draw an analogy between the change in the concept of time in the transition from classical to relativistic physics and the concept of consciousness (i.e., first-person experience) that supports eliminativism.

Speaking of extravagant positions, I also have a strong interest in panpsychist/neutral monist views, especially of the novel Russellian variety that recently has gained quite a bit of attention. As with plant cognition, I am skeptical about the truth of panpsychism, but a number of very interesting ideas are discussed in the relevant debates, and I am somewhat attracted to some of them, such as the idea that the natural sciences are concerned only with what the entities they talk about do, rather than what they are.

Computational Neuroscience

In my empirical research, I have worked on biologically inspired learning in recurrent artificial neural networks. I showed that a simple online learning procedure with a minimal error signal (1 bit only, basically indicating 'performance got better' or 'performance got worse') suffices to train such a network to perform rather complex tasks even without 'teacher forcing', i.e. without providing the network with the target output of the neuron during training to drive it into the required regime, given that the overall network dynamics is rather slow compared to the update frequency of the learning procedure. My article Emergence of Complex Computational Structures from Chaotic Neural Networks through Reward-Modulated Hebbian Learning, published in the journal Cerebral Cortex, describes the results of this work.

In collaboration with colleagues from the MPI for Biological Cybernetics in Tübingen, I analyzed electrophysiological recordings from macaque monkeys who performed a delayed matching-to-sample task. The monkeys were presented with an image and had to retain that image in memory for a few seconds. Then, another image was presented to them, and they had to decide whether the images were the same or different by releasing or not releasing a lever. Electrophysiological recordings were taken from extrastriate visual cortex (V4) and lateral prefrontal cortex. We found that during the memory period in between the presentation of the two images, oscillations in the theta frequency band (3-9 Hz) were synchronized between the two areas, and single unit activity ('spikes') was also phase-locked to these oscillations. The degree of inter cortical phase locking was predictive of the monkey's performance in the task. These results were published in the article Theta Coupling between V4 and Prefrontal Cortex predicts Visual Short-Term Memory Performance in the journal Nature Neuroscience. Moreover, we found directed coupling effects in the theta range between different sites within the extrastriate visual cortex during the memory period, as described in detail in the article Directed Coupling in Local Field Potentials of Macaque V4 during Visual Short-Term Memory revealed by Multivariate Autoregressive Models in the journal Frontiers in Computational Neuroscience.