Tapping into the Power of Visual Perception
As rightly said, “A picture is worth a thousand words”, the story is best told graphically rather than verbally. Important stories live in our data. Data visualisation is a powerful means to discover and understand these stories, and present them to others. Data visualisation is the graphical display of abstract information. The information is abstract means it describes the things that are not physical. The dedicated vision sense receptors in our body are approximately 70%.
Colin Ware explains how visual perception works and how it applies to data presentation. In what way can visualisation grab the attention of the viewers? The human visual system is a pattern seeker of enormous power and delicacy. The visual cortex of the brain performs parallel processing.
At higher levels of processing, perception and cognition are closely interrelating. However, the visual system has its own rules. We can easily see the patterns presented in a certain way if not they become invisible. Generally, when data is presented in certain ways the patterns can be readily perceived. If we can understand how perception works, our knowledge can be translated into rules for displaying information. Following perception‐based rules, we can present our data in such a way that the important and informative patterns stand out. If we disobey the rules, our data will be incomprehensible or misleading.
We’ll concentrate our look at visual perception in the following areas:
- Short‐term visual memory
- Visual encoding for rapid perception
- Gestalt principles of visual perception
We see from our eyes after our brain interprets what is sent. Our eyes are the sensory mechanisms through which light enters. It is translated by neurones into electrical impulses that are passed on to our brain. But our brain is where “perception” the process of making sense of what our eyes registers actually occurs.
Our eyes do not register everything that is visible in the world around us. It registers only what lies within their span of perception. A portion of what our eyes sense becomes an object of focus. Only through focus does what we see become more than a vague sense. A fraction of what we focus on becomes the object of attention or conscious thought. Finally, only a little bit of what we attend to gets stored away for future use. Without these limits and filters, perception would overwhelm our brains. Our memories store information starting from the moment we see something, continuing as we consciously process the information, and finally accumulating over years in a permanent storage area. The information remains ready for use if ever needed again that is until access to that information eventually begins to atrophy.
Memory comes in three fundamental types:
- Iconic memory (visual sensory register)
- Visual Short‐term memory (working memory)
- Long‐term memory (LTM)
People remember things in different ways. Iconic memory involves the memory of visual stimuli. It is how the brain remembers an image you have seen in the world around you. Example: Look at an object in the room, and then close your eyes and visualise that object. The image you “see” in your mind is your iconic memory of those visual stimuli. It is a type of sensory memory that lasts very briefly before quickly fading. It is assumed to last merely for milliseconds before disappearing.
Iconic memory is a lot like the ROM of a computer. Even though what goes on in iconic memory is preconscious, a certain type of processing known as pre-attentive processing occurs nonetheless. At an extraordinarily high speed, certain attributes of what we see are recognised during pre-attentive processing. It results in a particular set of objects being grouped together, all without conscious thought. Pre-attentive processing plays a powerful role in visual perception. We can intentionally design our dashboards to take advantage of this if we understand a bit about it.
Fig 1: Example of a graph that exceeds the limits of short-term memory.
Short-term memory is where the real work of sense-making is done. New data is passed in from the world through the senses and old data is swapped in from long-term memory. It works much faster than the conscious speed of thought to help us make sense of the world. Figure 1 exhibits a common problem in graph design: the meaning of the nine separate data sets—represented by the nine differently coloured lines—can’t be concurrently held in short term memory. The readers are forced to shift attention back and forth between the legend and the lines of data to remind them over and over what each line represents. If you want someone to make sense of the graph as a whole, then you must limit the number of data components that encode distinct meanings to seven at most—and safer yet, to no more than five.
One of Iconic memory’s key roles is- change detection of our visual environment which assists in the perception of motion. It is part of the visual memory system which also includes long-term memory and visual short-term memory.
Visual Short‐term memory
VSTM refers to the non-permanent storage of visual information over an extended period of time. Iconic memory is fragile, decay rapidly, and are unable to be actively maintained. Visual short-term memories are robust to subsequent stimuli and last many seconds. VSTM is distinguished from long-term memory, on the other hand, primarily by its very limited capacity. Visual Short‐term memory is where the information resides during conscious processing. The most important things to know about short‐term memory are:
- It is temporary.
- A portion of it is dedicated to visual information.
- It has a limited storage capacity.
The limited capacity of short‐term memory is also the reason why information that belongs together should never be fragmented into multiple dashboards, and scrolling shouldn’t be required to see it all. Once the information is no longer visible, unless it is one of the few chunks of information stored in short‐term memory, it is no longer available. If you scroll or page back to see it again, you then lose access to what you were most recently viewing? As long as everything you need remains within eye span on a single dashboard, however, you can rapidly exchange information in and out of short‐term memory at lightning speed.
Long-term memory (LTM)
It is the stage of the dual memory model proposed by the Atkinson-Shiffrin memory model. Informative knowledge can be stored for long periods of time. Long-term memory is commonly labelled as explicit memory (declarative), episodic memory, semantic memory, autobiographical memory, and implicit memory (procedural memory).
Visually Encoding Data for Rapid Perception
A limited set of basic visual properties is processed pre-attentively. Pre-attentive processing, the early stage of visual perception that rapidly occurs below the level of consciousness, is tuned to detect a specific set of visual attributes. Attentive processing is sequential, and therefore much slower. The difference is easy to demonstrate.
For many years vision researchers have been investigating how the human visual system analyses images. An important initial result was the discovery of a limited set of visual properties that are detected very rapidly and accurately by the low-level visual system. These properties were initially called pre-attentive since their detection seemed to precede focused attention. We now know that attention plays a critical role in what we see, even at this early stage of vision.
Example: Find the 4s
142577416687496357598475921765968474891728482 285958819829450968504850695847612124044 608365416496457590643980479248576960781
14257741687496357598475921765968474891728482 285958819829450968504850695847612124044 074674898985171495969124567659608020860 608365416496457590643980479248576960781
Much easier this time, wasn’t it? In this series the four could easily be distinguished from the other numbers, due to their differing colour intensity: the four are in red while all the other numbers are black, which causes them to stand out in clear contrast. Why couldn’t we easily distinguish the four’s in the first set of numbers based purely on their unique shape? Because the complex shapes of the numbers are not attributed that we perceive pre-attentively. Simple shapes such as circles and squares are pre-attentively perceived, but the shapes of numbers are too elaborate.
Attributes of Color
Fig 2: An example of searching for a target red circle based on a difference in hue:
(a) target is present in a sea of the blue circle distractors (b) target is absent
In fig 2 the visual system identifies the target through a difference in hue, specifically, a red target in a sea of blue distractors. Hue is not the only visual feature which is pre-attentive. In Fig 2 the target is again a red circle, while the distractors are red square.
Fig 3: An example of searching for a target red circle based on a difference in curvature:
(a) target is absent in sea of Red Square distractors (b) target is present
A unique visual property in the target allows it to “pop out” of a display. A target made up of a combination of non-unique features (a conjunction target) normally cannot be detected pre-attentively.
A common way to describe colour combines three attributes: hue, saturation, and lightness/brightness. Saturation measures the degree to which a particular hue exhibits its full, pure essence. The saturation of the red hue in Fig 4-5 ranges from 0% saturation on the left to 100% saturation on the right.
Fig 4: The full range of colour saturation with 0% saturation on the left and 100% saturation on the right.
Lightness (or brightness) measures the degree to which any hue appears, ranging from fully dark to fully light.
Fig 5: The full range of colour lightness with 0% lightness on the left (pure black) and 100% light on the right (pure white).
Intensity refers to both saturation and lightness. The illustration of colour intensity shows a circle that varies from the others not as a different hue but as a lighter (ie. less intense) version of the same hue. Both are different points along a colour scale that ranges from white (no red) to a rich dark shade of red (fully red).
Attributes of Form
In dashboard design, the attribute of line length is most useful for encoding quantitative values as bars in a bar graph. Line width, on the other hand, can be useful for highlighting purposes. You can think of line width as the thickness or stroke weight of a line. When lines are used to underline content or, in the form of boxes, to form borders around content, you can draw more attention to that content by increasing the thickness of the lines.
The relative sizes of objects that appear on a dashboard can be used to visually rank their importance. For instance, the greater importance of associated data is larger titles for sections of content, larger tables, graphs, or icons. Simple shapes can be used in graphs to differentiate data sets and, in the form of icons, to assign distinct meanings, such as different types of alerts.
Added marks are most useful on dashboards in the form of simple icons that appear next to data that need attention. Any simple mark (such as a circle, a square, an asterisk, or an X), when placed next to information only when it must be highlighted, works as a simple means of drawing attention. Last on the list of form attributes is an enclosure, which is a powerful means of grouping sections of data or, when used sparingly, highlighting content as important. To create the visual effect of an enclosure, you can use either a border or a fill colour behind the content.
Attributes of Position
The pre-attentive attribute 2‐D position is the primary means that we use to encode quantitative data in graphs (for example, the position of data points in relation to a quantitative scale). This isn’t arbitrary. Of all the pre-attentive attributes, differences in 2‐D position are the easiest and most accurate to perceive.
Attributes of Motion
As I type these words, I am aware of my cursor flickering on and off on the screen. Flicker helps us locate the cursor because it is a powerful attention‐getter. Evolution has equipped us with a heightened sensitivity to something that suddenly appears within our field of vision. Our ancient ancestors found it very valuable to become instantly alert when a saber‐toothed tiger suddenly sprang into their peripheral vision. Flickering objects on a screen is annoying, avoid it. Still, there are occasions when flicker is useful.
Gestalt Principles of Visual Perception
Back in 1912, the Gestalt School of Psychology began its fruitful efforts to understand how we perceive
pattern, form, and organisation in what we see. The German term “gestalt” simply means “pattern.” These
researchers recognised that we organise what we see in particular ways in an effort to make sense of it.
Their work resulted in a collection of Gestalt principles of perception that reveal those visual characteristics
that incline us to group objects together. These principles still stand today as accurate and useful
descriptions of visual perception and they offer several useful insights that we can apply directly in our
dashboard designs to intentionally tie data together, separate data, or make some data stand out as
distinct from the rest.
The following are the six principles:
So, this is the summary of the visualisation perception and its three fundamental types. To design dashboards that really work, you must always focus on the fundamental goal: communication. More than anything else, you must care that the people who use your dashboards can look at them and understand them easily and quickly. At Arima Research these constitute the core principles on which data dashboards and visual analytics projects are executed. The value is in the information and insights. These principles help us do convey the value much better and faster.
Source: Information Dashboard design- The effective Visual communication of data by Stephen Few