Persuasiveness & Abmissability of Demonstrative Evidence
It is well established that demonstrative evidence can be the most persuasive form of evidence. There are physiological reasons for this. As Drew R. Sinclair explains in * “Do You See What I Mean? Fundamentals of Visual Learning and Communication”:
"Most people are familiar with the basic operation of the eye. Light enters the retina, the retina converts the light to signals, and nerve fibers carry these signals to the brain for processing. A similar process exists for hearing.
While these processes are similar, their signal capacities are not. For vision, more than 1,000,000 nerve fibers carry information to the brain. By comparison, only about 30,000 nerve fibers carry auditory information. This superior “bandwidth” for visual information makes it the most powerful information conduit to the brain.
Inside the brain, visual information processing dominates over the other senses."
Darcy R. Merkur, in “Using Demonstrative Evidence to Get the Most Out of Expert Evidence”, Law Society of Upper Canada: Expert Evidence for Litigators, November 7, 2014, asks:
"So the question becomes, how do people best learn?
Recent studies have emphasized that we learn 75% of what we know through sight yet, while learning by sight is the most common means of learning, psychological studies indicate that after three days, most people will retain only 20% of what they see. By comparison, most people will only retain 10% of what they hear. However, when you simultaneous combine seeing with hearing, the retention rate three days later rises drastically to 65%.
The answer to how to help your experts in their role as educator is therefore to combine their oral testimony with visual aids."
* Drew R. Sinclair explains in “Do You See What I Mean? Fundamentals of Visual Learning and Communication” at 50, in The Oatley-McLeish Guide to Demonstrative Advocacy, (Markham ON: LexisNexis Canada, 2011).
Troy Lechman in “Demonstrative Evidence: The Law—Principles and Definitions”, explains as follows about the admissibility of demonstrative evidence:
Justice Dickson made the following comments about the law of evidence in R. v. Abbey:
The law of evidence, however, reposes on a few general principles riddled by innumerable exceptions. . . . There are also exceptions to the exceptions.
With such a description, it may seem as though understanding the law pertaining to demonstrative evidence is a daunting task. The key to understanding the law is to understand a few key general principles. They are as follows:
The demonstrative evidence must be relevant.
The demonstrative evidence must be accurate and fair.
The probative value of demonstrative evidence must outweigh any prejudicial effect of the evidence.
The demonstrative evidence must not offend any exclusionary rule.
These four principles apply equally to real evidence and demonstrative evidence. For demonstrative evidence, there is also an inquiry into whether the evidence is helpful in assisting the trier of fact understand the facts and evidence.
These principles all foster the underlying goals of the law of evidence. Those goals are to search for the truth, enhance efficiency in the trial process and to ensure fairness in the trial process. As Barbara Legate points out in a helpful article on the law relating to demonstrative evidence, questions of admissibility should always be answered with these goals in mind:
Evidence which meets these very fundamental goals ought to be admitted by the trial judge. Demonstrative evidence which assists the trier of fact in the search for the truth, enhances the efficiency of the trial process and is not excluded because of overriding prejudicial effect is admissible using this approach.
 Troy Lechman, “Demonstrative Evidence: The Law—Principles and Definitions”, at 32, in The Oatley-McLeish Guide to Demonstrative Advocacy, (Markham ON: LexisNexis Canada, 2011)