# Why did the developement of neural networks stop between 50s and 80s?

In a video lecture on the development of neural networks and the history of deep learning (you can start from minute 13), the lecturer (Yann LeCunn) said that the development of neural networks stopped until the 80s because people were using the wrong neurons (which were binary so discontinuous) and that is due to the slowness of multiplying floating point numbers which made the use of backpropagation really difficult.

He said, I quote, "If you have continuous neurons, you need to multiply the activation of a neuron by a weight to get a contribution to the weighted sum."

But the statement stays true even with binary (or any discontinuous activation function) neurons. Am I wrong? (at least, as long as you're in the hidden layer, the output of your neuron will be multiplied by a weight I guess). The same professor said that the perceptron, ADALINE relied on weighted sums so they were computing multiplications anyways.

I don't know what I miss here and I hope someone will enlighten me.

• Not answering your question directly, but I think a large contribution to the halted development was the lack of computing power. We simply couldn't easily test proposed methods because computers were too slow at the time Feb 25, 2021 at 3:03
• Multiplying real numbers by 1 and 0 is a lot different than multiplying it with another real number.
– user9947
Feb 25, 2021 at 3:06
• @Recessive thank you for the answer. I'll take it generally that there was a lack of computer power and not exactly the lack of computing power for multiplying floating numbers. Feb 25, 2021 at 3:17
• 0.33*1=easy, 0.33*0.79=tough.
– user9947
Feb 25, 2021 at 3:54
• @Daviiid Not necessarily, the GPU was only widely available in early 2000, which is what is primarily used now for fast floating point multiplication, so in the 50's-80's there was an even greater disadvantage to this than other problems. Feb 25, 2021 at 4:33

## 1 Answer

I will first address your main question "Why did the development of neural networks stop between 50s and 80s?" In 40-50s there was a lot of progress (McCulloch and Pitts); the perceptron was invented (Rosenblatt). That gave rise to an AI hype giving many promises (exactly like today)!

However, Minsky and Papert have proved in 1969 that a single-layer architecture is not enough to build a universal approximating machine (see e.g. Minsky, M. & Papert, S. Perceptrons: An Introduction to Computational Geometry, vol. 165 (1969)). That led to the first disappointment in "AI". Which lasted until several major breakthroughs in 1980s: the proof of universal approximating capabilities of multi-layer perceptron by Cybenko, the popularisation of backpropagation algorithm (Hinton and colleagues), etc.

I agree with LeCun that using continuous activation functions have enabled the backpropagation algorithm at the time. It is only recently that we have learned to backpropagate in networks with binary activation functions (2016!).

• Thank you for your answer! LeCunn also says in the same lecture that we can approximate any function with an SVM, is it related to the universal approximating machine you mentioned ? And do you perhaps know in which article it was proved that we can approximate any function with an SVM please ? And that's crazy how it's until recently researchers found a method to train networks with binary activation functions. Like it was theoretically known that backpropagation works with discontinuous functions but we weren't able to do so in practice. Mar 13, 2021 at 1:01
• He probably refers to the Universal approximation theorem en.wikipedia.org/wiki/Universal_approximation_theorem. You may want to read e.g. this article citeseerx.ist.psu.edu/viewdoc/… Mar 14, 2021 at 13:43
• Thank you for your clarification and for the article. (I tried to cite you penkovsky with the @ but it's not working I'm sorry) Mar 14, 2021 at 13:58
• Happy to help. You may want to accept the answer if you find it satisfying. Mar 14, 2021 at 13:59
• Yes that's right, I always forget to do it. Thank you ! Mar 16, 2021 at 0:01