Week 3

This week the articles are related to memory processes.

Chapter 13 made a good point in the beginning that human memory studies are often confounded by the previous experiences of participants, such as the memory strategies they learned and mnemonics, which vary from one individual to another. This has also been somewhat of a problem in some of our social cognition studies, when we asked participants to remember, for example, a social network. Participants came up with many different strategies and ways of visualizations, and although it’s not directly related to the questions we study, I often wonder if they were actually confounds. I wonder how other human memory researchers view or solve this problem…

Pertinent to this, the authors seem to assume that animals don’t have these kind of strategies and animal research are thus not confounded this way (he wrote “the study of human working memory is complicated by the fact that people vary considerably in the amount of pre-experimental experience … with memory strategies. … An alternative approach is to study memory processes in nonverbal organisms.”). We only know that human participants use memory strategies because they can tell us; animal subjects can’t, but that does not seem to be a good reason to assume they do not actually use memory “strategies” that vary individually. We know that animals probably don’t use any mnemonics related to languages, however, animals may also have various experience and use different non-verbal strategies to memorize things, which may still confound the studies. The author himself even mentioned a few memory strategies later in the chapter, such as animals positioning themselves towards the shown stimulus (Hunter, 1913), and pigeon having large individual differences during the delays of a memory task. Notably, one of the pigeons was clearly using a memory strategy (which amazed me) by pecking after a red sample and not pecking after a green sample, and then it performed well in the task. This is obviously an observable behavior, but we don’t really know if other pigeons had other strategies that they didn’t “tell” us. So it sounds somewhat unfair for the author to say that only human studies could be confounded by usage of different memory strategies…

I’m a bit confused by the descriptions of the delayed matching task in Skinner’s (1950) and W. A. Roberts’ (1972) studies. Based on my understanding, pigeons (in Skinner’s study) determine which comparison stimulus have the same color as the sample stimulus. The sample appears on the central button, and after a delay time, two comparison stimuli appear on the two side buttons (?). W. A. Roberts’ (1972) study is also quite unclear in that I didn’t understand why more than one response were required (what were pigeons responding to? Why was the accuracy worse when less responses were required?). The author mentioned that a number of responses were required to “initiate the delay”, which made it even more confusing… Assuming “delay” refers to the interval between the sample and comparison stimuli, then weren’t pigeons responding before the comparison stimuli even appear? What could they respond to?

The author then introduced theories concerning animal memory, including the trace strength, temporal discriminability, and association with reinforcement (none of which explain the memory process perfectly), followed by the directed forgetting paradigm, base-rate neglect and a series of related studies. It seems interesting that the paradigms here (and in other readings this week) are (almost) the same as the reinforcement/associative learning tasks we discussed last week, only with delays in the middle. Reinforcement learning is everywhere!

The next section of Chapter 13 and the other review paper (Animal models of episodic memory) both talk about episodic memory, so here I’ll refer to both of them together. I really like and agree with the Zentall’s argument that using unexpected questions is a better way to test for episodic memory, compared to the other options presented in Crystal’s paper. Most of the paradigms (What-Where-When Memory, Source Memory, Item-in-Context Memory) didn’t seem to provide compelling evidence that distinguish between semantic memory and episodic memory (mental time travel). Instead, I think results found those those learning paradigms could be perfectly explained without episodic memory, since they mostly just involve a variant of the reinforcement learning paradigm where the animal needed to figure out specific cues associated with the rewarded stimulus. The cue could involve “what”, “where”, “when”, “source”, or “context”, but there seemed to be no concrete evidence suggesting that these could not be memorized solely through semantic memory. In the Item-in-Context Memory paradigm, particularly, I believe the results could be simply explained by that rats were choosing a stimulus that were presented to them for a less number of times (blueberry was presented only once and strawberry was presented twice, so the answer was blueberry), which does not require episodic memory and does not support the author’s original hypothesis. Using unexpected questions, however, showed that pigeons and rats could actually recall what just happened (“did I just peck?” Or “was there food just now?”) in order to answer an unexpected question, without already trained extensively to answer this exact question. I also like the ingenious design of the unexpected-question experiments, which I wouldn’t see in a human study since researchers may just be lazy and ask subjects to self-report, rather than spending time on designing their study well.

Chapter 14 discussed the research on animals’ visual and auditory list memory, particularly in terms of the primacy and recency effects. The author mentioned that animal memory often show rapid forgetting within 1 minute. It makes me think that this fast forgetting could be due the abstract experimental task — probably no pigeon is genetically well-prepared to peck at buttons based on the colors they saw, since this doesn’t seem like a crucial skill for them to survive in nature. However, some abilities, such as remembering where their homes are, is quite crucial for certain pigeons and they could retain that memory for a lot longer than 1 minute, which may be due to that they are genetically programmed for that. I wonder if we can get pigeons who are superior on the delayed matching task by selectively breeding pigeons based on their performance, just like dog breeding… Of course this sounds non-practical and arguably non-ethical, but just theoretically a possible way to show that animals may have better memory on what they are genetically prepared to remember.

The topic of memory (and perhaps the topics of later weeks too) haven’t been extensively adapted to AI research yet, with the exception of the long short-term memory (LSTM) neural networks. LSTM networks are used in natural language processing, and pay “attention” to both the currently processed words (“short-term memory”) and its context (“long-term memory”). It sounds like this might be just another deep learning algorithm that only borrowed words from psychology but didn’t actually borrow much of the concept, though… Anyway, in terms of memory, robots still have a long way to go to simulate human or animal ability. It’s probably particularly interesting/hard when it comes to episodic memory — wouldn’t they need to first have a sense of self to be able to traverse back in their own time?