Game Levels & Controls

Main menu
Level 1: Default Game
Level 2: Captioned
Level 3: One Switch
Level 4: Blow Switch
Level 5: Keyword Switch
Level 6: Large Graphics
Level 7: High Contrast
Level 8: Simplified Graphics
Level 9: Non Visual - Discrete Movement
Level 10: Non Visual - Continuous Movement
Level 11: Experiment
Level 12: 2 Players
Level 13: Adjustable Difficulty

Main menu

Use the mouse or UP and DOWN to select a level, and the CLICK or press SPACE to play. In order to support one-switch access to the menu, the yellow selection frame automatically moves on every 3 seconds. The option currently focused is read aloud, so that the menu is accessible by people with vision impairments.

The following shortcuts are active at all game levels:

Key	Action
P	Pause/Resume game
F1	Return to the main menu
Esc	Exit
Home/End	Increase/decrease speech volume
Page Up/Page Down	Increase/decrease music volume
Insert/Delete	Insert/decrease sound FX volume

You can skip introductory screens by pressing any key or clicking the left mouse button.

Level 1: Default Game

This is a demonstration of the default game settings. Use LEFT, RIGHT and SPACE to play. Be careful! If you destroy the sun that passes by every now and then, the screen will turn black until either the sun comes out again, or you are destroyed.

Level 2: Captioned

This level includes captions for all in-game sounds. This option can be handy for people with hearing disabilities, or when playing with the sound turned off. Even sounds for elements that are not currently on-screen are captioned (e.g., warnings about the coming of the mothership and the sun). Two captioning options are offered: (a) graphic captions, where pre-rendered comic-book style graphics are used; and (b) text, where captions are rendered using the game’s embedded font. You can switch among the captioning options using F3. Use LEFT, RIGHT and SPACE to play.

Level 3: One Switch

The game is played using a single button (i.e., key). This type of gameplay is quite popular among motor-impaired people, but it is also useful for platforms that offer limited or hard to use controls, such as mobile phones. Furthermore, the simplicity of control offers great advantages for casual games and gamers. At this level, your spaceship constantly moves until it reaches the borders of the screen. Use SPACE to switch the direction of movement and simultaneously fire a bomb. Keep SPACE pressed for 3 seconds to access the pause menu. In order to support one-switch access to the pause menu, the yellow selection frame automatically moves on every 3 seconds.

Game speed can have a dramatic impact on the usability and fun of one-switch games. So, this level allows you to adapt the game speed to your needs. You can use numbers 6 and 7 to decrease game speed (6 = small speed change, 7 = larger speed change) and 8 and 9 to increase game speed (8 = small change, 9 = larger speed change). Press 0 (zero) to reset game speed to its initial value.

Level 4: Blow Switch

This level is a variation of Level 3, where instead of the keyboard a standard microphone is used, thus allowing hands-free gaming. Blow gently into the microphone to switch the direction of movement and simultaneously fire a bomb. At the bottom-right end of the screen there is a blow-strength indicator. When the bar reaches the top, a “switch” command is issued. Although initially designed as an accessibility feature, game testing results showed that this was a very popular feature among all players.

Level 5: Keyword Switch

At this level, you can type 'LEFT' to go left, 'RIGHT' to go right, 'FIRE' to fire and 'PAUSE' to pause. Oddly, this level is also included in Game Over! as a demonstration of a potential accessibility problem. It was included in Terrestrial Invaders is because it provides an alternative way to game control that can be used for educational purposes. For example, as suggested by domain experts, it can be used by children with cognitive impairments for learning to associate words to directions and actions. Furthermore, it can be employed by learners of all ages to learn spelling or touch typing. In this case, the keywords used may continuously change, e.g., you have to type a word spoken by a commentator, or written on the enemy spaceships, etc.

Level 6: Large Graphics

As suggested by its title, the game graphics have been enlarged to allow comfortable viewing by people with some types of visual disabilities. You can use both the mouse and the LEFT, RIGHT and SPACE keys to play. Furthermore, you can change the graphics size until you find the one that suits you best. Press 2 to decrease the graphics size, 3 to increase it and 1 to reset it to the default value.

Level 7: High Contrast

As Level 6, this level is also targeted to people with visual disabilities. Two different modes are supported: (a) bright graphics on dark background; and (b) dark graphics on bright background. You can switch among these by using F9. High contrast can be combined with the use of simple shapes, instead of the game’s graphics (see Level 8 for more details). Press F8 to turn them on and off.

Level 8: Simplified Graphics

Simple (e.g., rectangles, ellipses), single-colored shapes are used to render all game graphic elements. This option can be useful to people with severe visual impairments, by allowing them to replace detailed graphics with big blobs with high-contrast solid colors used in combination with 2D sound and audio descriptions. Additionally, simple shapes can also be handy to people with some types of cognitive impairments, gamers playing on a small screen, as well as very young children.

Level 9: Non Visual - Discrete Movement

This level is targeted to blind people, gamers playing without a screen or anyone who wants to sharpen his/her auditory skills. In order to make the game easier, all spaceships (yours and the enemies) move in 5 discrete positions. Enemy spaceships and bullets are augmented with a discrete looping sound. Game sounds are localized on the 2D plane based on the player's position. Two parameters are used to achieve that: (a) panning (i.e., left/right position of the sound); and volume (i.e., the closer to you, the louder it gets). Level gameplay instructions and menus are read aloud, as well as critical events, e.g. "shield deactivated". If you want to try this level, it is recommended that you use a set of headphones. You can use F7 to turn 2D sound on and off.

In addition to that, the game offers two experimental types of audio descriptions that verbalise the relative position of attacking spaceships in relation to the player, and warn for incoming fire. Use F4 to cycle among the available audio description options. All voices have been deliberately speeded up, in order to shorten the required speaking time and provide timely feedback. The two options are:

Summarizing description: a voice announces how many alien spaceships are in front, to the left and to the right of your spaceship. If there are no aliens in a particular direction, then this direction is not mentioned. Thus, for example, you would hear something like "left 2, front 1", or "right 1". On top of that, if there are any incoming bullets in front of your spaceship, a female voice repeats the word "danger".
Detailed description: Each enemy spaceship continuously announces its position. For example, there might be 2 spaceships, where one says "front, front, front, …", and the other "right, right, right, …". On top of that, if there are any incoming bullets, a female voice repeats "danger". Although when there are more than 2 enemies on the screen there is quite some fuss that may lead to confusion, practice showed that this method has significant value, and a potential for great improvement, e.g., by using different voices in order to take advantage of the "cocktail party effect".

Level 10: Non Visual - Continuous Movement

This level is similar to Level 9, but all spaceships move in a continuous scale, just like in the default game. Thus, this level is considerably harder to play.

Level 11: Experiment

This level is similar to the first one, but you can try any combination of the adaptations introduced in all the previous levels, thus creating a unique version of the game, fully customized according to your preferences and needs. An overview of the available options is provided below:

Key	Action
F2	Mouse ON/OFF
F3	Cycle captioning options
F4	Cycle audio description
F5	Automove ON/OFF
F6	Mic. switch ON/OFF
F7	2D sound ON/OFF
F8	Simple graphics ON/OFF
F9	Cycle contrast options
6,7	Decrease game speed
8,9	Increase game speed
0	Reset game speed
2	Decrease graphics size
3	Increase graphics size
1	Reset graphics size
Insert	Increase sound FX volume
Delete	Decrease sound FX volume
Home	Increase speech volume
End	Decrease speech volume
Page Up	Increase music volume
Page Down	Decrease music volume

Level 12: 2 Players

This level showcases the concept of Parallel Game Universes . Player 1 (pink spaceship on the left) in order to play uses LEFT, RIGHT & SPACE. Player 2 (blue spaceship on the right) plays in one-switch mode, using TAB to fire and switch direction.

Except that, there are several differences among the 2 players. More specifically:

Player 1:

starts with 3 lives;
can only destroy red planes and the mothership;
can be destroyed by any enemy;
can not have more than 2 bombs concurrently active in the game;
drops smaller, slower moving, bombs than Player 2;
moves faster than Player 2;
plays against a larger number of more aggressive enemies than Player 2.

Player 2:

starts with 5 lives;
can only destroy blue planes and the mothership;
can only be destroyed by blue planes;
can not have more than 3 bombs concurrently active in the game;
drops much larger and faster bombs than Player 1;
moves slower than Player 1;
plays against a smaller number of less aggressive enemies than Player 1.

If any of the two players loses all his/her lives, the game is over.

Level 13: Adjustable Difficulty

In this level several difficulty adjustment facilities are offered. These can be activated through the pause menu (by pressing 'P'), or during gameplay by pressing the following shortcuts:

Key	Action
L	Get an extra life
D	A random enemy is destroyed
S	Activate shield
U	Decrease the size of your bombs
I	Increase the size of your bombs
T	Decrease speed of the enemy spaceships
Y	Increase speed of the enemy spaceships
W	Decrease the number of enemy bullets that can be concurrently active
E	Increase the number of enemy bullets that can be concurrently active
Q	Reset the number of enemy bullets that can be concurrently active
6,7	Decrease overall game speed
8,9	Increase overall game speed
0	reset game speed