Error while digital reading sensors

Question

I'm trying to digitally read all separate 8 sensors from a QTRA 8-sensor board:

http://www.pololu.com/docs/0J19/all

The problem I'm getting is that although the robot can read its position correctly:

qtra.readLine(sensorValues);

and it can read the first 6 sensors digitally correctly, it doesn't read anything from the first 2.

Below you have my simplified code that I wrote to test this out. Note that light7 and light 8 always return 0, even when directly on top of the black line. I'd like to know if there's anything I'm doing wrong and any way to avoid manually assigning 1 or 0 to the outputs of those first 2 sensors.

    #include <QTRSensors.h>

#define NUM_SENSORS             8   // number of sensors used
#define NUM_SAMPLES_PER_SENSOR  4  // average 4 analog samples per sensor reading
#define EMITTER_PIN             2  // emitter is controlled by digital pin 2

// sensors 0 through 5 are connected to analog inputs 0 through 5, respectively
QTRSensorsAnalog qtra((unsigned char[]) {A7, A6, A5, A4, A3, A2, A1, A0}, 
  NUM_SENSORS, NUM_SAMPLES_PER_SENSOR, EMITTER_PIN);
unsigned int sensorValues[NUM_SENSORS];

//LIGHTS
int light1 = A0;
int light2 = A1;
int light3 = A2;
int light4 = A3;
int light5 = A4;
int light6 = A5;
int light7 = A6;
int light8 = A7;


void setup(){
  pinMode(light1, INPUT);
  pinMode(light2, INPUT);
  pinMode (light3, INPUT);
  pinMode(light4, INPUT);
  pinMode(light5, INPUT);
  pinMode(light6, INPUT);
  pinMode(light7, INPUT);
  pinMode(light8, INPUT);

  Serial.begin(9600);
}

void loop(){
  Serial.print(digitalRead(light1));
  Serial.print(".....");
  Serial.print(digitalRead(light2));
  Serial.print(".....");
  Serial.print(digitalRead(light3));
  Serial.print(".....");
  Serial.print(digitalRead(light4));
  Serial.print(".....");
  Serial.print(digitalRead(light5));
  Serial.print(".....");
  Serial.print(digitalRead(light6));
  Serial.print(".....");
  Serial.print(digitalRead(light7));
  Serial.print(".....");
  Serial.print(digitalRead(light8));
  Serial.println();
}

Thanks to anyone who will take the time to answer this...

Answer 1

The problem was that the sensors are designed in one 2 - sensor module and another 6 - sensor module.

I had to artificially introduce "digital read" by comparing values from the analogRead function.

i.e.

 if(analogRead(light7) > value){
        return 1;
}else{
     return 0;
}