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Why Left 4 Dead Works
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Why Left 4 Dead Works

December 21, 2010 Article Start Page 1 of 4 Next

[What makes the Left 4 Dead series' gameplay design work so well for players? This comprehensive design analysis analysis from Full Sail grad student Paul Goodman and course director Adams Greenwood-Ericksen takes developer commentary and matches it against the SRK Framework, a tool for categorizing cognitive behavior in interactive media.]

Mechanics are the core building blocks of any game. They are the primary method by which players are able to operate in a game environment to overcome the challenges and obstacles that a game's developers have placed down. Yet in their design a crucial factor can be overlooked with regards to how game mechanics are made or adjusted through the development process: understanding the ways in which players think and learn about the function of game mechanics is key to determining their effectiveness.

If a mechanic is too complex for players to understand, the result may be player frustration, whereas if a mechanic is too simple, it can quickly lead to player boredom and repetitive gameplay. By using established methods of assessing and modeling cognitive behavior, game designers might gain better insight into the likely thought processes of players, enabling them to improve the quality of mechanics in game.

One such method, the Skills, Rules, and Knowledge Framework (SRK), which was first presented by Jens Rasmussen in 1983, focuses on categorizing different types of cognitive behavior across three different levels.

  • Skill based behaviors are activities that are common and routine for an experienced individual and do not require much attention to execute; instead, the process is "triggered" and carried out in an automated fashion. An example of a skill based behavior common to console gamers is using the left and right thumbsticks to look around and move an avatar in game.
  • Rules based behaviors hinge on following known mental steps and checklists built to guide the activity and require individuals to put more effort into carrying them out. Preparing to load a saved game on a console is be an example of a rules-based behavior, as it follows a checklist of steps to navigate through menus to find the appropriate saved game file and load it.
  • Knowledge based behaviors present players with an activity with which they have little or no prior experience or understanding, and therefore must undertake some form of research (e.g. reading manuals or checking forums) or problem solving (e.g. trial and error experimentation) oriented approach to gain more information. A longtime gamer who's never played any form of major MMORPG, for example, would very likely engage in knowledge-based behavior in order to understand the functions of a typical interface from that particular game genre.

A strength of the SRK framework is that it is broadly applicable to virtually all interactive activities. Therefore, in the context of electronic gaming, players of a particular video game will engage its mechanics using cognitive behaviors that can be assessed and classified by designers using the SRK Framework.

Therefore, game designers can use this tool to identify how players engage a game mechanic during gameplay. Through reviewing how players move from a knowledge based behavior to rule based or skill based behaviors (or vice versa), designers can assess the effectiveness of a game mechanic and make adjustments as necessary, such as simplifying or adding complexity to the mechanic itself.

An example of a game that was developed with clear emphasis on what and how players think can be found in Valve's Left 4 Dead, released in 2008, and its sequel Left 4 Dead 2, released a year later in 2009. An action/survival first person shooter, L4D puts the players in control of four survivors battling their way to safety during a zombie apocalypse.

Hordes of "Infected" bar their path at every turn throughout the four campaigns, and working together as a team is often the only way players are able to achieve success, especially as many of the challenges posed by game mechanics and obstacles players face require more than one individual to complete.

Left 4 Dead

Early design of Left 4 Dead came about in 2004 after the release of Valve's classic tactical shooter Counter-Strike: Source. According to L4D team member Mike Booth, while experimenting with the AI for non-player bots the dev team found that the concept of "Small team of friends against hordes of clawing enemies" had a great deal of potential. Through more playtests and design discussion, the framework was laid down for Left 4 Dead core concept of a "Co-op vs. the horde game."

Players of L4D find themselves battling against the Infected, victims of a quickly and highly contagious plague that's ravaging the U.S. At their disposal, players start off with a pistol (with unlimited ammo) and a default melee attack for pushing enemies away; throughout each campaign players find more weapons ranging from pump-action shotguns to fully automatic assault rifles, as well as improvised items in the forms of Molotov cocktails and pipe bombs.

Common Infected are the most frequently encountered enemy type within the game, located almost everywhere in each campaign. They appear as normal people, albeit with glowing eyes and bleached skin. The average Infected is a fast runner, can move through most terrain and over most obstacles and assault players with punches and kicks. However, they die fairly easily with a few well placed shots to their chest, head, legs or arms (the horror movie standard of zombies dying only from head wounds having been thrown out).

They also are lacking any sense of self-preservation, and will run through and into hazards and obstacles, including fires and live explosive devices. Occasionally, common Infected attack in large groups (referred to by players as a "Horde") and try and overwhelm the players using their superior numbers. This can be a random occurrence or triggered by a scripted "crescendo" event, usually caused by players having to overcome an environmental obstacle such as a lowering a bridge or destroying a barricade.

The common Infected serves a variety of different purposes, the most obvious of which is to serve as the main enemy type opposing players, but also to provide experience with core gameplay dynamics such as the use of the weapons and items at the player's disposal.

The simplicity of the common Infected allow new players to L4D to quickly evolve during their normal progress through the game environment from knowledge-based behaviors involving research and experimentation intended to determine how common Infected act, to using rule or skill-based behaviors to quickly and efficiently overcome even large numbers of these basic enemies.

Article Start Page 1 of 4 Next

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